






,6*^ \,'*^^**A* *-t,°'-fS'*\<? %.'*^^V* 















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CHEMISTRY OF PULP 
AND PAPER MAKING 



BY 

EDWIN SUTERMEISTER, S. B. 



NEW YORK 

JOHN WILEY & SONS, Inc. 

London: CHAPMAN & HALL, Limited 
1920 



6 



<%% 



COPYRIGHT, 1920 
BY 

EDWIN SUTERMEISTER 



Manufactured in the U. 5, A . 

©CI.A605113 

DEC 24 1920 



JD ( ^ o / ^ 



PREFACE 

The preparation of this book was undertaken because it was 
felt that there was need of a work dealing primarily with the 
chemical aspects of the pulp and paper industry and embodying 
under one cover the results of recent investigations along this 
line. The endeavor has been to include all details which the 
chemist should have to enable him to grasp the methods of 
manufacture, but it is not intended to be a treatise on paper 
making in all its mechanical phases, and in fact the mechanical 
features of the industry are discussed only in so far as they are 
necessary for a satisfactory understanding of the chemistry 
involved. It has been written chiefly with the idea of helping 
the young technical man, whether chemist or chemical engineer, 
and it has therefore been assumed that the reader has a fair 
knowledge of the elements of chemistry. At the same time it 
has been attempted to write as simply and plainly as possible 
and it is believed that any one connected with the pulp and 
paper industry will find it helpful and suggestive. 

The subject matter has been collected from personal notes 
and experiences during the author's twenty years' service as 
chemist in the industry, as well as from a careful review of the 
literature relating to the subject. The latter is often contra- 
dictory in the extreme and in certain cases it has proved almost 
impossible to reconcile conflicting statements. In such cases 
both sides of the argument have been presented as fairly as 
possible. It is peculiar to the industry that there are usually 
a large number of variable factors which influence any one 
operation, and since it is practically impossible to control all 
of these variables it necessarily follows that results in different 
mills will not be in harmony. For this reason it is expected 
that the observant reader will find statements to which he 



IV 



PREFACE 



will take exceptions, but such differences of opinion are often 
desirable since they indicate lines of investigation which will 
lead to a better understanding of many things which are at 
present obscure. 

Regarding the methods of analysis and testing which are 
given it may be said that the attempt has been made to include 
all which are necessary for routine work in controlling opera- 
tions. There are many occasional analyses which it is necessary 
to make during special investigations, but it is impractical to 
include all of these and for such methods reference must be 
made to the numerous standard text-books of analytical 
procedure. 

Acknowledgment is made of the assistance of Mr. J. L. Merrill 
on the subject of "Straw" and also of that of my associates at 
the mills of S. D. Warren Company, whose encouragement has 
helped to overcome many difficulties. 

I am also indebted to the publishers of Van Nostrand's Chem- 
ical Annual for a number of the tables which will be found in 
the appendix. 



CONTENTS 



CHAPTER I Page 

Cellulose * 

Physiological and Physical. Composition and Constitution. Cellulose 
and Water. Solvents. Cellulose and Salts. Decomposition by Acids, 
Alkalis, Oxidants, Ferments and Heat. Compounds, Nitrates, Gun- 
Cotton, Nitrites, Acetates, Sulphuric Esters. Mixed Esters, Benzoates, 
Formates, Alkali-Cellulose. Sulpho-Carbonates. Groups of Celluloses. 
Compound Celluloses. Methods of Determination. 

CHAPTER II 

Fibrous Raw Materials 34 

The Vegetable Cell. Seed Hairs. Bast Fibres. Fibres from Whole 
Stems. Woods. Length of Fibres. Densities and Composition of 
Woods. Bark and Knots. Decay. Woods used in Pulp Making. 
Bulk of Raw Materials. 

CHAPTER III 

Rags, Esparto, Straw, Bamboo 68 

Grades of Rags. Dusting. Boiling. Boilers. Losses. Esparto. Clean- 
ing. Boilers. Cooking. Bleaching. Alkali Recovery. Straw. Com- 
position. Cooking with Lime. Soda Cooks. Bamboo. Sources. 
Analyses. Cooking. Fibres from Old Papers. 

CHAPTER IV 

The Soda Process 93 

Raw Materials. Digesters. Causticizing. Lime Mud. Cooking Liquor. 
Boiling. Effect of varying Steam Pressure, Strength of Cooking Liquor, 
Alkali Added, and Time of Cooking, Speed of Reaction. Soda 
Consumption. Yields. Modified Processes. Relief gases. Blow 
Tanks. Wash Pits and Washing. Black Liquor. Recovery of Soda. 
Evaporators. Incinerators. Black Ash Waste. Losses. Tests and 
Analyses. 

CHAPTER V 

The Sulphate Process I 4- 1 

Kraft Fibre. Cooking. Liquor Composition. Yields. Odors. Blow-off 
Gases. Black Liquor. Soda Recovery. Smelting. Composition of 
Melt. Tests and Analyses. 



vi CONTENTS 

CHAPTER VI Page 

The Sulphite Process 156 

Theory. Wood and its Preparation. Liquor Making. Sulphur Burning. 
Burning Pyrites. Absorption Apparatus. Quality of Lime Desired. 
Losses. Composition of Acid. Storage. Digesters and Linings. Boiling. 
Mitscherlich Process. Ritter-Kellner Process. Records and Charts. 
Relieving Gas. Following the Progress of a Cook. Recovery of Gas. 
Blowing the Charge. Washing. Composition of Products. Modified 
Processes. By-products and Waste Liquor. Tests and Analyses. 

CHAPTER VII 

Ground Wood or Mechanical Pulp 212 

Outline of Process. Grinders. Factors Influencing Results. Steamed 
Wood. Woods Available. Enge Process. Examination of Product. 
Bleaching. 

CHAPTER VIII 

Bleaching 225 

Properties of Chlorine. Gas Bleaching. Hypochlorites. Bleaching 
Powder and its Solutions. Electrolytic Bleach. Principles of Bleaching. 
Weight of Fibre Lost on Bleaching. Change in Color on Bleaching. 
Use of Backwater. Bleaching Systems. Ground Wood. Antichlors. 
Washing Bleached Pulp. Permanganate Bleaching. Effect on Strength 
and Chemical Properties of Stock. Testing Bleaching Powder. 

CHAPTER IX 
Sizing 257 

Necessity for Sizing. Surface Sizing. Gelatine and its Testing. Starch. 
Rosin. Source and Properties. Size Making. Reactions of Sizing. 
Rosin Required. Defects in Rosin Sizing. Testing Rosin and Sizes. 
Alum. Preparation. Composition. Testing. Casein Sizing. Glue 
Sizing. Rubber Resins. Mitscherlich Process. 

CHAPTER X 

Loading and Filling Materials 290 

Reason for Using. Effect on Sizing. Qualities Desired. Retention. 
Clay. Gypsum. Pearl Hardening. Precipitated Chalk. Talc. Asbes- 
tine. Heavy Spar. Testing. 

CHAPTER XI 

Coloring 306 

Importance. Pigments. Natural Mineral Colors. Artificial Mineral 
Colors. Natural Organic Colors. Artificial Organic Colors. Union of 
Dye and Filler. Effect of Water on Dyes. Direct Cotton Colors. Basic 
Colors. Eosines and Rhodamines. Acid Colors. Organic Pigments. 
Calender Staining. Testing Colors. 



CONTENTS Vli 

CHAPTER XII Page 

Coated Papers 325 

Advantages and Disadvantages. Body Stock. Applying the Coating. 
Influence of Adhesives. Finishing Coated Papers. Glue Requirements 
for Coating. Casein, Source and Composition. Solvents. Preservation 
of Solutions. Testing. Albumen. Starch. Modified Starches. Clay. 
Blanc Fixe and Barytes. Satin White. Accessories. 

CHAPTER XIII 

Water 351 

Importance in Paper Making. Classification and Sources. Color. 
Boiler Scale Formation. Water Softening. Filtration. Methods of 
Sampling and Analysis. 

CHAPTER XIV 
Testing Wood Pulps 368 

Moisture in Baled Pulps. Lap Pulp. Strength or Beating Test. Color 

Comparison. Bleaching Properties. Loss in Weight on Bleaching. 

Sedimentation Test. 

CHAPTER XV 
Paper Testing 386 

Microscopic Examination. Fibre Content. Unbleached Sulphite. 

Physical Tests. Machine Direction. Wire Side. Weight per Ream. 

Thickness. Bulk. Opacity. Gloss. Tensile Strength. Stretch. 

Bursting Strength. Folding Endurance. Tearing Test. Absorbency. 

Volume Composition. Air Permeability. Grease-proof Properties. 

Degree of Sizing. Chemical Tests. Ash. Retention. Sizing Materials. 

Rosin Determination. Parafhn. Chlorine. Free Acid. Sulphur. 

Amount of Coating. Glue or Casein Determination. Unbleached 

Fibers. Ground Wood. 

CHAPTER XVI 

Printing 429 

Definition. Half-tone Plates. Lithography. Paper for Different Types 
of Printing. Choice of Inks. Defects and their Causes. 

Appendix 444 



CHEMISTRY OF 

PULP AND PAPER MAKING 



CHAPTER 1 
CELLULOSE 

Even at the present day the chemistry of cellulose cannot be 
said to be well understood though much energy has been ex- 
pended in the attempt to discover its secrets and several com- 
prehensive books have been written on the subject. 1 This state 
of affairs is due largely to its colloidal characteristics which 
make it very difficult to prepare and isolate pure compounds, 
and render it practically impossible to determine its molecular 
weight or to ascertain its structural formula. For these reasons 
the matter in the present chapter is confined largely to state- 
ments of facts and any extended discussion of theoretical con- 
siderations is intentionally avoided. 

Physiological and Physical. Cellulose is the chief product of 
vegetable life and forms so large and important a part of all 
plant structures that its formation in the vegetable world is 
said to be synonymous with growth. It is practically the non- 
nitrogenous skeleton of all plants, but it never occurs in the 
plant in the free state, being associated or combined with fats 
and waxes, coloring matters, tannins, etc. Because of its physi- 
cal properties and its relative inertness toward the attack of 
chemicals cellulose is of enormous commercial importance, form- 

1 Cross and Bevan: Cellulose, London, 1918; Researches on Cellulose, 1895- 
1900, London, 1901; Researches on Cellulose, 1900-1905, London, 1906; Re- 
searches on Cellulose, 1905-1910, London, 1912. Schwalbe: Die Chemie der 
Cellulose, Berlin, 191 1. 

1 



2 CELLULOSE 

ing, as it does, the basis of the paper making and textile in- 
dustries, and being used in modified forms in the manufacture 
of high explosives, artificial silk, and celluloid products. 

In the industrial world the term "cellulose" is generally- 
understood to mean the portion remaining after vegetable tis- 
sues have undergone thorough alternate treatments with alka- 
line solvents and oxidizing agents, and our knowledge of the 
chemical nature of cellulose is based upon a study of materials 
isolated by more or less drastic treatment of this nature from 
fibrous raw materials. The typical cellulose is that obtained 
from cotton by the textile bleaching processes, which remove 
the non-cellulose substances with which it is associated in the 
plant. When thus prepared it is a white substance, with a 
specific gravity of about 1.45, and with the general shape and 
characteristics of the fibres from which it was prepared. The 
individual fibres are translucent when seen under the microscope 
but masses of them are more or less opaque. 

Composition and Constitution. The elementary composition 
of purified cotton cellulose is 

Per cent 

Carbon 44-4 

Hydrogen : 6.2 

Oxygen 49. 4 

which corresponds to the empirical formula C 6 Hi O5. This does 
not take into account the mineral constituents which are always 
present to a greater or less extent even in the most highly purified 
material. The ash in cotton cellulose is usually 0.1 to 0.2 
per cent but this may be reduced to as little as 0.05 per cent by 
digestion in hydrofluoric and hydrochloric acids and washing 
very thoroughly in pure water. Ash constituents, on the other 
hand, may be taken up by cellulose from solutions with which 
it is in contact and various observers have shown that it is 
capable of removing from solution small amounts of the oxides 
of aluminum, iron, chromium, tin and lead. Materials taken 
up in this manner must not be confounded with the normal 
mineral matter. 



CELLULOSE AND WATER 3 

As already mentioned the constitutional or structural formula 
for cellulose has not yet been definitely established although 
many investigators have attempted to solve the problem and 
have proposed various formulae based upon its known reactions 
and their products. Among those proposed that of Green * is 
as follows: 

CH (OH) • CH - CH (OH) 

\ \ 
o o 

/ / 
CH (OH) • CH - CH 2 

This is intended to represent cellulose only in its simplest or 
unpolymerized form, as, for instance, in ammoniacal copper 
solution. The cellulose of fibres may be composed of a number 
of these groups, joined by means of their oxygen atoms, or 
merely a physical aggregate of a number of molecules of the 
above composition. 

By other authorities cellulose is regarded as a polycyclohexane 
derivative or as an essentially labile aggregate which assumes 
various configurations according to the action of the reagents 
employed. It is closely related to the sugars, starches, glucose 
and other members of the carbohydrate family. 

Cellulose and Water. Water at ordinary temperatures, or 
even at a temperature corresponding to 60 lbs. steam pressure, 
has no action on cotton if air is excluded, but a mixture of air 
and steam causes rapid disintegration of the fibre. 2 

.Air dry cellulose retains variable amounts of water of con- 
stitution according to the humidity and temperature of the 
surrounding atmosphere. With normal cotton this constitu- 
tional moisture amounts to 6 to 8 per cent, but if the cotton has 
been hydrated by mercerization, by dissolving and reprecipi- 
tating, or by prolonged abrasive action in the presence of water, 
its capacity for retaining moisture is increased and such air 

1 A. G. Green: Z. Farben- u Textil-Chem., 1904, 3, 97-98. 

2 Hebden: J. Ind. Eng. Chem., 19 14, 6, 714-720. 



4 CELLULOSE 

dry fibre may retain 9 to 10 per cent of water. Acids which 
cause condensation (HC1, HBr), influence this change in the 
opposite direction and the resulting product has a lower moist- 
ure capacity — 3 to 5 per cent — than the normal cellulose. 
Since the atmospheric humidity affects the moisture content of 
cellulose it is obviously essential to have some fixed standard 
for commercial transactions and for the paper industry it is 
the practically universal custom to consider that air dry 
wood pulp contains 10 per cent of moisture, i.e., 100 parts of 
air dry pulp will yield 90 parts of bone dry fibre when dried at 
ioo° C. 

A knowledge of the normal moisture content of cellulose, and 
of the products made therefrom, is of importance in the finishing 
and commercial handling of textile goods, while in the paper 
industry the hydration effect of the beating process determines 
very largely the character of the paper made. In the latter 
industry it is possible to make from the same raw materials, by 
varying the beating process, such widely different products as 
blotting paper and grease-proof parchment. Ignorance of the 
relation of cellulose and atmospheric humidity is also one of 
the chief causes of trouble in printing plants where the paper- 
maker's product becomes the publisher's raw material. 

The difference between cellulose hydrates and hydrocellulose 
is one which is often not well understood and about which 
much confusion is likely to arise. Hydrocelluloses are formed 
by hydrolytic action, — as by acids, — and are characterized 
by the presence of free carbonyl groups which reduce Fehling's 
solution. They are also distinguished by an abnormally low 
moisture content, as noted above, and are soluble to a con- 
siderable extent in sodium hydroxide solutions at the boiling 
temperature. Cellulose hydrates may be formed, either with or 
without simultaneous hydrolysis, if cellulose is acted upon by 
alkalis or other chemicals which exert a swelling action in the 
presence of water. They are widely different in their properties 
but possess the common characteristics of a high moisture con- 
tent, and a decreased resistance to hydrolysis by acids. Ost and 



CELLULOSE AND SOLVENTS 5 

Westhoff l do not recognize the existence of " water of hydra- 
tion" as distinct from hygroscopic moisture and believe that the 
latter can be accurately determined at 125 C. They find that, 
after drying at 120 to 125 C, mercerized cotton, normal cotton, 
and regenerated cellulose from viscose all have the same elemen- 
tary composition. 

Cellulose and Solvents. Cellulose is insoluble in all neutral 
solvent liquids; it is, however, dissolved by: 

1. Concentrated zinc chloride solutions (40 to 50 per cent 

ZnCl 2 ), when heated to 80 to 100 degs., or at lower 
temperatures if the cellulose has previously been 
hydrated. 

2. Zinc chloride dissolved in twice its weight of hydro- 

chloric acid (35 per cent HC1). 

3. Solutions of cuprammonium hydrate. 2 

These three solvents dissolve cellulose without transforming it 
into other compounds, except those formed by the action of 
water, and from solvents 1 and 3 the cellulose may be quanti- 
tatively regenerated although in the hydrated condition. When 
fibrous celluloses are dissolved by these reagents they pass 
through various stages of swelling and hydration until finally a 
uniform structureless solution is obtained. One characteristic 
of these solutions is their high viscosity which limits the amount 
of cellulose which can be dissolved to a filterable solution to 
about 7 to 9 per cent. When the solution of cellulose in zinc 
chloride is forced through a small orifice into alcohol the cellu- 
lose is precipitated in the form of a continuous thread of trans- 
parent, solid matter containing zinc oxide which can be re- 
moved by treating with hydrochloric acid. Water also causes 

1 Ost and Westhoff: Chem. Ztg., 1909, 33, 197. 

2 These may be prepared conveniently by precipitating cupric hydrate by 
adding caustic soda to a cold solution of copper sulphate, washing the precipitate 
thoroughly, and then dissolving it in strong ammonia (sp. gr. 0.90). The solu- 
tion should contain 2.5 to 3.5 per cent of copper (as CuO • nH 2 0), and 15 per cent 
of NH 3 (as NH4OH). 



6 CELLULOSE 

the precipitation of cellulose but in an even more hydrated state. 
The solution in cuprammonium is not at all stable, the cellulose 
being readily precipitated by alcohol, sodium chloride and other 
salts of the alkalis, and even by sugar. 

Solutions of cellulose find technical application in making 
threads, which are carbonized for use in incandescent lamps, 
and in the manufacture of artificial silk, etc. The action of 
solvents is also utilized in making "vulcanized fibre" or "press- 
board" where a web of fibre is passed through a zinc chloride solu- 
tion and then wound up on a mandrel or drum. After removal 
from the drum the chemicals are thoroughly washed out and 
the sheets are dried and used as insulating material or in struc- 
tural work. The superficial action of cuprammonium solutions 
may be utilized in water-proofing fabrics, as in the case of the 
"Willesden" products, but if, as in the case of these goods, no 
attempt is made to remove the hydrated copper, the products 
will have a greenish color. 

Cellulose is hydrated and dissolved by sulphuric acid of a 
strength of 67.0 to 78.0 per cent H 2 S0 4 , — approximately H 2 S0 4 • 2 
H 2 — H2SO4 • 3 H 2 0. The solution is syrupy and nearly color- 
less and if diluted at once the cellulose is precipitated as a gelati- 
nous hydrate. This reaction is the basis for the production of 
"parchment paper" or "vegetable parchment" in which a con- 
tinuous web of pure cellulose paper is passed first through a bath 
of acid and then at once into water which stops the action of the 
acid and reprecipitates the cellulose which has been superficially 
dissolved. After washing out the last traces of acid the parch- 
mentized web is treated with a solution of glucose or glycerine 
and dried. The glycerine serves to retain moisture and make 
the paper less brittle than it would be if entirely dried out. 
Paper treated by this parchmentizing process suffers consider- 
able linear shrinkage, sometimes as much as 20 per cent, and 
also loses somewhat in weight. 

Deming 1 has shown that cellulose is also soluble in concen- 
trated aqueous solutions of certain salts, such as antimony tri- 

1 H. G. Deming: J. Am. Chem. Soc, 1911, 33, 1515-1525. 



CELLULOSE AND SALTS 7 

chloride, stannous chloride and zinc bromide. Solutions of these 
salts, and many others, in aqueous hydrochloric acid dissolve 
cellulose with still greater ease. From such acid solutions there 
are obtained by reprecipitation "modified celluloses," amorphous 
products which have distinct reducing properties and are readily 
hydrolyzed. 

Although ordinary hydrochloric acid, and even that of sp. gr. 
1. 1 96, are incapable of dissolving cellulose, it has been shown 
by Willstatter and Zechmeister x that complete solution rapidly 
takes place on treating cellulose with fuming hydrochloric acid 
of a specific gravity of 1.2 or over. Cotton or filter paper may 
be dissolved in acid of sp. gr. 1.209 in about 10 seconds. Im- 
mersing the cotton and kneading with the acid enables solu- 
tions of 7 to 15 per cent strength to be obtained according to 
the strength of the acid. Such solutions are colorless and clear 
and if diluted within 30 to 45 minutes after preparation a form 
of cellulose is quantitatively precipitated and the solution has 
no cupric reducing power. 

Cellulose and Salts. Because of its colloidal properties cellu- 
lose forms characteristic combinations with inorganic oxides, 
particularly those of aluminum, chromium, iron, tin and lead. 
These oxides are taken up by cellulose from solutions of their 
salts and the fibres which are thus mordanted possess increased 
affinity for coloring matters. In the case of iron salts sufficient 
ferric oxide may be taken up by the fibre to seriously injure 
its color. 

This ability to absorb oxides doubtless plays some part in 
the sizing of paper, for Schwalbe and Robsahm 2 found that 
unbleached sulphite wood pulp was capable of absorbing all 
the alumina present in 3 per cent of its weight of aluminum 
sulphate. This corresponds to an absorption of about 0.46 
per cent of A1 2 3 on the weight of the fibre. A similar investi- 
gation by Sutermeister, 3 working on bleached fibres, showed 

1 R. Willstatter and L. Zechmeister: Ber., 1913, 46, 2401-2412. 

2 C. G. Schwalbe and H. Robsahm: Wochbl. Papierfabr., 1912, 43, 1454-1457. 

3 E. Sutermeister: Pulp Paper Mag. Can., 1913, 11, 803. 



8 CELLULOSE 

that the weight of A1 2 3 absorbed, based on the bone dry fibre, 
was 0.23 to 0.29 per cent for soda poplar, 0.00 to 0.17 per cent 
for sulphite spruce, and 0.10 to 0.13 per cent for rag fibres 
(cotton). 

Rassow x finds that cotton cellulose is capable of absorbing 
small quantities of copper from dilute solutions of copper salts 
and that the absorbed metal cannot be removed by washing. 
The amount absorbed was independent of the time of contact, 
the strength of the solution or its temperature. Similar results 
were obtained with solutions of nickel sulphate, aluminum sul- 
phate and potassium chloride. 

Decompositions of Cellulose. Cellulose is broken down in a 
number of different ways according to the nature of the attack- 
ing substance, its concentration and the physical conditions 
accompanying the reaction, yet the study of these decomposi- 
tions and their products has done but little to explain the con- 
stitution of the cellulose molecule. 

Acids. Dilute sulphuric and hydrochloric acids, and acids in 
general, attack cellulose with varying degrees of rapidity de- 
pending on the temperature and the concentration of the acid. 
The products of such action are either soluble substances, 
chiefly dextrins and dextrose, or insoluble bodies generally 
termed hydrocelluloses. These are disintegrated residues, more 
or less retaining the form of the original fibres, and they differ 
from cellulose in the presence of free aldehydic groups and in 
the ease with which they are acted on by alkalis. According 
to Griffin and Little 2 hydrocellulose absorbs oxygen when 
heated, even at so low a temperature as 50 degs., and after 
being kept for some hours at 80 to 100 degs. in contact with 
air is converted into dark colored compounds which are soluble 
in water. Hydrocellulose, unlike oxycellulose, does not attract 
basic dyes. 

Ville and Mestrezat 3 found that dilute hydrofluoric acid had 

1 B. Rassow: Z. angew. Chem., 1911, 24, 1127. 

2 Griffin and Little: Chemistry of Paper Making, 114. 

3 Ville and Mestrezat: Compt. rend., 19 10, 150, 783. 



ALKALIS 9 

little effect on cellulose but that at 40 to 50 per cent strength 
considerable dextrose was formed. Ost and Wilkening 1 have 
confirmed Flechsig's claim that 98 per cent of the cellulose may 
be converted into dextrose by suitable treatment with acid. 
This result cannot be reached by the action of dilute acids at 
high temperatures because the dextrose formed is destroyed 
either by reverse condensation or by conversion into acids. 
According to Willstatter and Zechmeister 2 cellulose may be 
completely hydrolyzed by hydrochloric acid acting in the cold 
for a period of 1 to 2 days and a yield of 95 to 96 per cent of 
the theoretical amount of dextrose may be obtained. Cun- 
ningham 3 has reinvestigated the relationship of cellulose to 
dextrose and has failed to confirm the results of Ost and Wilken- 
ing or Willstatter and Zechmeister; he considers their conclu- 
sions based on insufficient data and thinks that the investiga- 
tions have thrown very little light on the structure of the 
cellulose complex. 

The formation of friable hydrocelluloses by acids is of great 
importance industrially for upon it is based the carbonization 
process for separating cotton from wool in which the mixed 
goods are immersed in acid and allowed to dry without washing. 
This converts the cotton into hydrocellulose which can be re- 
moved by dusting, leaving the wool behind in suitable condition 
for future use. 

Alkalis. In the presence of air caustic soda solutions of a 
strength of 10 to 20 grams per liter rapidly disintegrate cotton 
fibre at a temperature corresponding to 10 lbs. steam pressure. 
When air is excluded cellulose is only slightly acted on by dilute 
solutions of alkalis even at high temperatures. Caustic soda 
solutions of 12 per cent strength, and over, combine with cellu- 
lose at ordinary temperatures, causing marked changes in physical 
structure but not breaking up the molecular grouping. Still 
stronger solutions, at temperatures as high as 180 degs., form 

1 Ost and Wilkening: Chem. Ztg., 1910, 34, 461. 

2 Willstatter and Zechmeister: Ber., 1913,46, 2401. 

3 Cunningham: Chem. Soc. Trans., 1918, 113, 173-181. 



10" CELLULOSE 

merely soluble modifications which on diluting and acidifying 
are precipitated in colloidal form. At still higher temperatures 
(250 degs.) and with larger proportions of alkaline hydroxides 
cellulose is broken down largely into acetic and oxalic acids. 

Oxidants. From the condition of papers and textiles which 
have for centuries been exposed to all ordinary atmospheric 
conditions, it seems fair to assume that oxidation due to the 
surrounding atmosphere is extremely slight, a fact which is of 
the utmost importance technically. Cellulose is also quite re- 
sistant to oxidizing agents in dilute solutions, a circumstance 
which makes it possible to remove impurities of a colored nature 
without at the same time destroying the fibres. If, however, 
the concentration of the oxidant exceeds the limit of resistance 
of the cellulose destructive oxidation takes place with the forma- 
tion of products of low molecular weight, principally oxalic 
and carbonic acid. Not all of the products are soluble, how- 
ever, as a portion remains undissolved and retains more or less 
of the original form of the fibres. These insoluble residues are 
known as oxy celluloses. They contain free aldehydic groups, 
are easily hydrolyzed, and yield some furfural, C4H3O • COH, 
on boiling with hydrochloric acid of sp. gr. 1.06. They are 
white, friable substances and contain less carbon and more 
oxygen than cellulose. No method is known of restoring to its 
original condition fibre which has been converted to oxycellulose. 

The results of the oxidation of cellulose are not always the 
same, as they depend on the nature of the oxidant, its concen- 
tration, the temperature at which it acts and on accompanying 
reactions of a hydrolytic nature. With concentrated solutions 
of hypochlorites or hypobromites there is some formation of 
chloroform and carbon tetrachloride or the corresponding bro- 
mine compounds. The action of nitric acid (sp. gr. 1.1 to 1.3) 
at elevated temperatures results in the formation of a series of 
oxycelluloses which are characterized by yielding less furfural 
than those formed by the action of chromic acid. With chromic 
acid the degree of action depends on the proportion of the re- 
agent and on the hydrolytic action of the associated mineral 



OXIDANTS II 

acid. The oxycelluloses produced yield comparatively large 
amounts of furfural. The ultimate result of the action of 
chromic acid in the presence of sulphuric acid is complete com- 
bustion to C0 2 and H 2 0, a reaction upon which are based quan- 
titative analytical methods. 

After a study of the results obtained in bleaching Cross and 
Bevan * suggested the possibility of the formation of a cellulose 
peroxide. Similar phenomena were observed by Ditz 2 in the 
case of cellulose which had been gradually heated to 8o° C. in 
an acid solution of a persulphate and then slowly cooled, while 
according to Cunningham and Doree, 3 ozone rapidly attacks 
cotton with the formation of cellulose peroxide which is decom- 
posed by water at 8o° C. 

Oxycelluloses reduce Fehling's solution and on this property 
is based Schwalbe's method for determining the degree of bleach- 
ing of fibres; as hydrocelluloses reduce Fehling's solution, the 
method also shows the effects of any coincident hydrolytic 
action. The determination of the degree of bleaching, or, as it 
is frequently called, the " copper number," has proved of con- 
siderable assistance in technical investigations and the procedure 
employed by Schwalbe 4 is about as follows: Two portions of 
about three grams each are weighed out, of which one is used 
for the determination of the percentage of moisture. The other 
is reduced to a finely divided condition and mixed with 300 c.c. 
of water and 100 c.c. of Fehling's solution. This is boiled in a 
flask for exactly 15 minutes, using a reflux condenser to keep 
the volume constant and a stirrer to maintain continuous agi- 
tation. Precautions must be taken to prevent overheating 
the walls of the flask as drops of the liquid or portions of the 
moist fibre which spatter onto them may be decomposed with 
formation of products affecting the results. After boiling, the 

1 Cross and Bevan: Z. angew. Chem., 1906, 19, 2101. 

2 Ditz: Chem. Ztg., 1907, 31, 833. 

3 Cunningham and Doree: Chem. Soc. Proc, 19 12, 28, ^8. 

4 Schwalbe: Ber., 1907, 40, 1347-1351; Z. angew. Chem., 1910, 23, 924-928; 
Z. angew. Chem., 1914, 27, 567-568. 



12 CELLULOSE 

liquid is filtered while hot by means of the suction pump, and 
the fibrous residue is washed with hot water. The precipitated 
copper is dissolved from the fibre by nitric acid, the final traces 
being removed by digestion with ammonia, and the copper then 
determined by electrolysis. 

As the presence of hydrated or modified celluloses causes the 
precipitation of copper hydroxide by adsorption the " copper 
number" obtained as above must be corrected by deducting 
the "hydrate copper value" which is determined by immersing 
a fresh portion of the cellulose in cold Fehling's solution for 
45 minutes and determining the copper as before. 

Ferments. Certain organisms affect the complete disruption 
of the cellulose molecule, or aggregate, the chief products being 
hydrogen, methane, carbon dioxide and fatty acids. Such bac- 
terial fermentation on a large scale in the soil is one of the chief 
processes by which the cellulosic portion of plant remains is 
resolved into simpler products. In the digestive organs of her- 
bivorous animals cellulose is broken down by similar fermenta- 
tive processes, apparently with the formation of simpler sub- 
stances of high nutritive value, which are readily assimilated. 
In addition to these, gaseous products are also formed, carbon 
dioxide, methane, and sometimes hydrogen being produced. 

Omelianski concluded that the organisms causing decompo- 
sition of cellulose were anaerobic, but Kellerman and McBeth 1 
have succeeded in isolating three cellulose-destroying organisms 
which act most rapidly under aerobic conditions. None of 
these causes evolution of gas. In addition they have isolated 
eleven other species of cellulose-destroying bacteria all of which 
were facultative anaerobes fermenting cellulose most rapidly 
under aerobic conditions. 

Heat. When cellulose is heated above 250 C. very complex 
decompositions take place and among the products are charcoal, 
acetic acid, methyl alcohol, acetone, furfural, carbon monoxide 
and carbon dioxide. The proportions of these substances vary 
with the temperature and the rate and duration of heating. 

1 Kellerman and McBeth: Centr. Bakt. Parasitenk, II, 34, 485-494. 



NITRATES 13 

When cellulose was distilled destructively in such a way that a 
temperature of 100 degs. was reached in i| hours and 500 degs. 
in 7 to 8 hours, Bantlin x found the following products, the per- 
centages being given on the weight of the dry substance used: 

Per cent 

Coke 3 2 - 9 

Water 31. 7 

Tar.... 3-25 

Acetic acid 3-28 

Aldehydes 5- 82 

Ketones o. n 

Carbon dioxide n . 26 

Carbon monoxide 4-78 

Ethylene o. 24 

Hydrogen o. 02 

Ethane o. 35 

Methane • . . o. 68 

Undetermined 5. 23 

During the course of this distillation there was an exothermic 
reaction at 250 to 300 degs. which was complete at 320 degs. 

Compounds of Cellulose. Cellulose is not a substance of 
great reactivity yet there are a number of its compounds which 
are of very great commercial importance. Most of these, it is 
true, do not vitally concern the paper maker, yet a discussion 
of the properties of cellulose, no matter how concise, would be 
quite incomplete unless they were at least briefly mentioned. 
Moreover, a knowledge of how they are formed and of their 
characteristics is of distinct assistance in enabling the student 
to secure a better perspective of paper making processes in 
their relation to those of other industries. 

Nitrates. These esters are formed by direct reaction with 
nitric acid, usually mixed with sulphuric acid, and the compo- 
sition and properties of the resulting nitrate depend largely on 
the proportions of the two acids and on the amount of water 
with which they are mixed. Crane and Joyce, 2 using a mixture 

1 G. Bantlin: J. Gasbel., 1914, 57> 3 2 and 55. 

2 Crane and Joyce: J. Soc. Chem. Ind., 1910, 29, 540. 



I 4 CELLULOSE 

containing 57 to 67 per cent of sulphuric acid, 16 to 6 per cent 
of nitric acid and 25 to 27 per cent of water, and nitrating for 
short times have prepared products with as little as 3.5 to 4.5 
per cent of nitrogen. These are pasty, gelatinous masses, in- 
soluble in all nitrocellulose solvents, but readily soluble in 
solutions of caustic alkalis. 

When stronger acids are employed the nitrates formed con- 
tain more nitrogen up to a limit of about 14 per cent which 
corresponds to the trinitrate, GeE^C^NC^. This nitrate, 
which is the most explosive gun-cotton, may be prepared by 
treating cotton with a mixture of 3 parts of nitric acid (sp. gr. 
1.5) and 1 part of sulphuric acid for about 24 hours at io° C. 
The unstable mixed esters, containing both nitric and sulphuric 
groups, are formed as an intermediate stage in the reaction and 
the NO3 groups finally replace the HS0 4 groups. It is con- 
sidered that traces of the mixed ester remaining in the finished 
product are often responsible for its instability. In this reaction 
100 parts of cellulose yield about 170 parts of the nitrate. Nitra- 
tion under these conditions does not visibly alter the physical 
structure of the cellulose. The trinitrate is insoluble in alcohol, 
ether, mixtures of the two, glacial acetic acid or methyl alcohol; 
it is very slowly soluble in acetone. The next lower members, 
corresponding approximately to the dinitrate, C 6 H 8 05(N03)2, 
are soluble in ether-alcohol, acetic ether, acetic acid and methyl 
alcohol, while the mononitrate, C6H9O5NO3 is very soluble in 
ether-alcohol, acetic ether and absolute alcohol. A consider- 
able number of nitrates have been formed but it has proved 
very difficult to isolate any one of them in a pure condition and 
from a careful study of the work of G. Lunge, 1 Cross and Bevan 
have reached the conclusion that " the stages of nitration of 
cellulose are not molecular stages, but represent progressive 
increments of the esterifying groups in a mass-aggregate, which 
is the reacting unit." 2 

The general properties of the cellulose nitrates are: (1) nitric 

1 G. Lunge: J. Am. Chem. Soc, 1901, 23, 527. 

2 Cross and Bevan: Researches on Cellulose, II, 1900-1905, 44. 



GUN-COTTON 15 

acid may be removed by warming with alkaline solutions, the 
amount removed depending on the concentration of the alkali; 
(2) nearly all of the nitric acid is expelled by treatment with 
cold concentrated sulphuric acid; (3) boiling with ferrous sul- 
phate and hydrochloric acid drives off the nitrogen as nitric 
oxide; (4) alkaline sulphydrates, ferrous acetate and numerous 
other substances convert the nitrate into ordinary cellulose. 

The various cellulose nitrates find many very important com- 
mercial uses. Mixed with castor oil they are extensively used 
in the manufacture of artificial leather. In solution in ether- 
alcohol cellulose nitrate is employed in the manufacture of 
artificial silk by the Chardonnet process, the fibre being finally 
denitrated by treatment with ammonium sulphide to render it 
less inflammable. The fibrous nitrates may be reduced to plastic 
masses by kneading with solvents and in this condition may be 
formed into articles of any desired shape. As films they find 
use in photography, as the carrier for the emulsion; in the solid 
form, after the incorporation of camphor, they are spoken of as 
celluloid or xylonite and find innumerable uses. 

The nitrogen content of the nitrates for various purposes is 
given by Mork 1 as follows : Celluloid and films for moving pic- 
tures about io| to n| per cent; varnishes and lacquers n| to 
12 per cent; for powder purposes 12 to 12! per cent; and for 
gun-cotton 13 to 14 per cent. In the higher nitrates the pro- 
portion of oxygen is such that upon decomposition the products 
are entirely gaseous and it is upon this property that their use 
as explosives depends. 

Gun-cotton. Because of the similarity between many of the 
methods used in paper making and those in the manufacture of 
gun-cotton a very brief description of the methods used in the 
latter industry may be of interest. 

Cotton is still practically the only cellulose used although it 

has apparently recently been demonstrated that certain grades 

of wood pulp will make acceptable substitutes. The cotton is 

obtained in the form of spinning wastes or of the short fibres 

1 Mork: J. Frank. Inst., Sept., 1917. 



I 6 CELLULOSE 

from the seeds known as linters. Where spinning wastes are 
used the fibres are first degreased by treatment with some 
solvent, then boiled with caustic soda, bleached with bleaching 
powder solution or with calcium sulphide, washed, neutralized 
with sulphuric or hydrochloric acid, again washed, and finally 
dried. It should contain no chlorides, sulphates, oxycellulose 
or hydrocellulose, but it often contains mechanical impurities 
such as wood, string, colored threads, metal, etc., and to re- 
move these it is hand picked as it passes along a conveyor to a 
" willow" which opens out the lumps and knots. After leaving 
the "willow" it is again hand picked and then is dried by hot 
air, weighed in charges of the desired size and cooled in closed 
containers. 

Various methods of nitration are in use but all depend on 
the immersion of small quantities of cotton in comparatively 
large volumes of mixed nitric and sulphuric acid. The time 
of nitration varies from 30 minutes to 24 hours according to the 
method employed. The speed of nitration increases rapidly 
with rise of temperature, but the yield decreases although the 
nitrogen content of the product remains practically constant. 
After nitration the excess acid is removed by centrifugal action 
and the fibrous nitrate is washed by rinsing and is then boiled 
either with water alone or with the addition of a very little 
alkali in order to remove traces of free acid and to decompose 
and dissolve unstable impurities. This boiling operation, with 
intermediate washings with cold water, sometimes lasts 4 to 5 
days. 

The next operation is that of pulping the washed nitrate; 
this is done in beaters very similar to those used in paper manu- 
facture but slightly modified in order that thorough agitation 
and no settling may take place. During the pulping the fibre 
is reduced in length and is at the same time washed continu- 
ously with hot water in order to remove the last traces of acid. 
Further washing is given by agitation, settling and removing 
suspended impurities after which enough alkali is added to 
leave in the finished gun-cotton 1 to 2 per cent of alkaline matter 



ACETATES I 7 

calculated as CaC0 3 . The pulp is then run into moulds with 
bottoms of fine wire gauze and the water removed by suction 
and by hydraulic pressure. The slabs thus formed are used 
wet or after drying according to the purpose for which they are 
desired. 

For the manufacture of smokeless powder the washed pulp 
is screened and then dried by centrifugal action; it still con- 
tains much water and this is removed by treatment with ethyl 
alcohol. Finally a little ether, or other volatile solvent, is 
kneaded in which produces a paste ready for the blocking 
operations. The solvents are removed during drying so that 
very little remains in the finished product. 

Nitrites. When viscose silk is treated with nitrous gases in 
the presence of nitric acid nitrites of cellulose are formed. They 
are not soluble in water, alcohol, acetone, ether, chloroform, or 
ethyl acetate. Nitrogen is given off slowly at ordinary tem- 
peratures and rapidly on heating. Nitrites are liable to occur 
in nitrocellulose and cause rapid deterioration. 1 

Acetates. Cellulose acetates are formed when cellulose is 
treated with acetic anhydride under quite widely varying con- 
ditions. The monoacetate, which is formed at no degs., is 
insoluble in all neutral solvents and in the solvents of cellulose. 
At 140 to 160 degs. higher acetates are formed, accompanied 
by solution in the reaction mixture, while in the presence of 
catalytic agents — zinc chloride, sulphuric acid, or phosphoric 
acid, for instance — the reactions take place at much lower 
temperatures, due doubtless to the formation of hydrocellulose 
which acetylates more rapidly than the normal cellulose. Ost, 2 
who has studied the formation of acetates by three different 
processes, finds that all yield the triacetate, CeH^Os^HsC^, 
but at the same time he doubts the existence of a triacetate of 
normal cellulose and considers these compounds as derivatives 
of a series of hydrocelluloses. This feature of preliminary 
hydrolysis seems to be one of the essentials of acetate forma- 

1 Nicolardot and Chertier: Compt. rend., 1910, 151, 719-722. 

2 Ost: Z. angew. Chem., 1906, 19, 993. 



l8 CELLULOSE 

tion. Acetylation of the fibrous celluloses without appreciable 
structural change may be accomplished by diluting the reagents 
with hydrocarbons. 

The higher acetates are soluble in acetone, phenol and chloro- 
form and the solutions are of high viscosity. Boiling the ace- 
tates with alkaline solutions splits off the acetyl groups and 
the cellulose is regenerated. 

In contrast to the nitrates the acetates are non-explosive, and 
since they can be dissolved by appropriate volatile solvents to 
homogeneous solutions they are admirably adapted for use in 
the preparation of films, threads, etc. Commercial acetates 
are on the market in the fibrous, granular or powdered forms 
or in solutions of various viscosities. They are used for nearly 
all purposes for which the nitrate is used except for explosives 
and their use would be still more extended but for the fact that 
their cost of manufacture is appreciably greater than that of 
the nitrate. It is interesting to note that acetate silk is the 
only one in which the final product retains the ester composi- 
tion, since in other cases reactions take place which leave the 
thread simply as hydrated cellulose. This is probably the 
reason why wetting reduces the strength of acetate silk so much 
less than it does the other kinds. 

Cellulose-Sulphuric Esters. The action of concentrated sul- 
phuric acid on cellulose causes the formation of a series of esters 
which have been described as cellulose sulphuric acids but 
which are more probably derivatives of resolution products. 
The first stage of the reaction is, according to Stern, 1 the forma- 
tion of a disulphuric ester, C 6 H 8 03(S04H) 2 , which is soluble in 
water while its calcium barium and lead salts are insoluble in 
alcohol. This reaction of cellulose and sulphuric acid is of 
great importance in processes of esterification, where the acid 
acts as a catalyst, first combining with the cellulose and then 
being replaced by the ester forming groups. In the case of 
nitrates and acetates this substitution is never quite complete, 
and traces of SO4H remain fixed in both compounds. The 

1 Stern: J. Chem. Soc, 1895, 1, 74-90. 



FORMATES 1 9 

presence of such residues 'in the nitrate renders it unstable and 
its removal is one of the chief reasons for the extended boiling 
and washing treatments which gun-cotton undergoes. 

Mixed Esters. As may be concluded from the above the 
joint action of sulphuric acid with other esterifying agents can 
result in the formation of mixed esters containing SO4H groups 
as well as other negative groups. In this way aceto-sulphates 
are formed by the action of acetic anhydride, glacial acetic 
acid and sulphuric acid. 1 These contain from 5 to 25 per cent 
of combined S0 4 and may be grouped in three classes ac- 
cording to their physical properties. Those with most S0 4 are 
soluble in water, the others in acetone or dilute alcohol. In a 
similar way aceto-nitro-sulphates and nitro-benzoates have been 
formed. 

Benzoates. The action of benzoyl chloride in the presence of 
alkali hydroxides results in the formation of cellulose benzoates. 
The monobenzoate is formed with only slight structural changes 
when cellulose is treated with a 10 per cent solution of caustic 
soda and shaken with benzoyl chloride. The dibenzoate is 
formed in the presence of 15 per cent caustic soda solution, the 
fibrous celluloses being disintegrated, as the dibenzoate is an 
amorphous substance. This compound is soluble in acetic acid 
and chloroform. 

Formates. Formylated cellulose may be made by treating 
hydrocellulose with formic acid in the presence of zinc chloride. 2 
Its slight solubility in organic solvents and its lack of thread, 
and film-forming ability make it rather unpromising. Accord- 
ing to German patents, 3 solutions of the following compounds 
may be used as solvents of cellulose formate: iodides and bro- 
mides of the alkali metals, metallic nitrates as well as those of 
ammonia and the alkaline earths, cupric chloride, soluble bichro- 
mates, alkali xanthates, aniline salts and alkali salts of aromatic 
mono- and polysulphonic acids. 

1 Cross, Bevan and Briggs: Berl. Ber., 1905, 38 and 1859. 

2 Worden: J. Soc. Chem. Ind., 1912, 31, 1064. 

8 Ger. Pats. 266,600 and 267,577, July 5, 1912, and Feb. 26, 1913. 



20 CELLULOSE 

Alkali-Cellulose. The action of solutions of sodium hydroxide 
of 12 to 15 per cent strength causes considerable change in the 
structure of fibrous celluloses, particularly cotton which is 
changed from a flattened twisted ribbon with a large central 
canal to a thickened cylinder in which the canal shows very 
little. When this action takes effect on cloth there is a con- 
siderable shrinkage both in length and width but at the same 
time the cloth gains in strength. The amount of shrinkage 
varies with the strength of solution employed; it is practically 
uniform for solutions of sp. gr. 1.00 to 1.10, while there is a 
sudden increase at sp. gr. 1.10 to 1.12. Between this point and 
sp. gr. 1.225 there is a relatively rapid increase in shrinkage 
but beyond the latter point the shrinkage again diminishes. If 
the goods are kept under tension during the reaction the physi- 
cal changes give to the material a peculiar, silky lustre. This 
reaction is spoken of as mercerization from the name of Mercer 
by whom it was first discovered. 

The effects thus obtained are due to a definite chemical com- 
bination of cellulose and caustic soda in the proportions C 6 Hi O5 
to 2 NaOH, accompanied by combination with water. This 
compound is entirely dissociated by water, the alkali being 
recovered unchanged while the cellulose remains in the hydrated 
condition. When it is treated with alcohol equilibrium is 
reached when part of the alkali is removed, the residue being 
C 12 H 2 oOio • NaOH. 1 

Cellulose-Sulpho-Carbonates. The above mentioned alkali- 
cellulose-hydrate, containing 30 per cent cellulose, 15 per cent 
caustic soda and 55 per cent water, is the first step in the forma- 
tion of cellulose-sulpho-carbonate which is also known as sodium- 
cellulose-xanthate and viscose. This compound is prepared by 
acting on the alkali cellulose with carbon disulphide at ordinary 
temperatures. In practice bleached cotton or wood pulp is 
treated with an excess of 15 to 18 per cent caustic soda solution 
and then pressed until it retains 2\ to 3 times its weight of the 
solution. This is then treated in a closed vessel with carbon 
1 Cross and Bevan: Researches on Cellulose, II, p. 13. 



CELLULOSE-SULPHO-CARBONATES 21 

disulphide amounting to about half the weight of the cellulose. 
At the end of about three hours at ordinary temperatures water 
is added and the mass allowed to stand for some hours to com- 
plete its hydration; on stirring a homogeneous solution results, 
which may be diluted to any desired degree. 

The impure compound is yellow in color due to by-products 
of the reaction, but the pure material, which may be prepared 
by treating the crude solution with alcohol or saturated brine, 
is obtained in the form of greenish white flocculent masses. 
These redissolve in water to a faintly yellow solution and from 
such solutions the xanthates of the heavy metals may be pre- 
cipitated by adding solutions of the corresponding heavy metal 
salts. 

Viscose solutions may be evaporated at low temperatures to 
solids which are completely resoluble in water, but if the solu- 
tions are heated to 70 to 80 degs. they thicken and at 80 to 90 
degs. coagulation takes place very rapidly. Mineral acids neu- 
tralize the total alkali in the viscose and cause precipitation of 
hydrated cellulose while organic acids are not sufficiently strong 
to decompose the sulpho-carbonate. 

The most characteristic property of viscose is its spontaneous 
decomposition with formation of hydrated cellulose, caustic soda 
and carbon disulphide or its reaction products. With aqueous 
solutions of greater strength than 1 per cent cellulose this de- 
composition causes the formation of a jelly of the shape and 
volume of the containing vessel. This jelly gradually contracts 
with the expulsion of water. Observations on 100 c.c. of a 
5 per cent solution kept in a stoppered vessel at ordinary temper- 
atures showed the following rates of coagulation and shrinkage. 1 
(See table on p. 22.) 

The cellulose regenerated from viscose differs from the original 
in being more hygroscopic, as well as being hydrated, and in 
being more reactive toward bases but less so toward acid groups. 

Viscose finds extensive use in the manufacture of artificial silk 
and in the preparation of films for transparent wrappings. 

1 Cross and Bevan: Text-Book of Paper Making, 3rd ed., p. 25. 



22 



CELLULOSE 



These latter are very thin, o.ooi inch, and as compared with 
nitrate or acetate films are much more water-absorbent. 



Coagulation 

First appearance of liquid 



Time in days 



8th day 
nth 
1 6th 
20th 
25th 
30th 
40th 
47th 



Vol. of cellu- 
lose hydrate 



83 5 
72.0 
58.0 
42.8 
38.5 



Diff. from 100 
c.c. = vol. 
expressed 



16.5 
28.0 
42.0 
57-2 
61. s 



The Groups of Celluloses. Up to this point the remarks have 
applied chiefly to cotton, which may be considered as the typical 
cellulose, but there are also numerous other celluloses which 
differ more or less widely from this standard. The fibrous 
celluloses, for instance, are grouped, according to C. F. Cross, 
into three classes, depending upon their degree of resistance to 
hydrolytic and oxidizing actions, the amount of furfural which 
they yield when boiled with dilute hydrochloric acid, and their 
elementary composition as regards the ratio of carbon to oxygen. 
The characteristics of the three groups may be tabulated as 
follows : 





A 
Cotton group 


B 

Wood cellulose 

group 


C 

Cereal cellulose 

group 


Hygroscopic moisture 

Elementary composition 

C:0 
Furfural 


6-8% 
| 44.0-44.4 

i 5 ° 
0.1-0.4% 

J No active 
I CO groups 


9-"% 
43.0-43.5 

5i 
3-6% 

Some free CO 
groups 


10-12% 
41.5-42.5 
53 
12-15% 
Considerable re- 
activity of CO 
groups 


Other characteristics 



In group A are included cotton, flax, hemp, rhea (ramie), 
sunn hemp, etc. They are usually associated in the plant 
world with substances easily removed by digestion with alkalis. 



COMPOUND CELLULOSES 23 

The purified celluloses of this group are considered chemically 
identical with cotton. 

Group B comprises celluloses obtained by the decomposition 
of compound celluloses, i.e., those from woods and lignified 
tissues in general. They may be considered as oxidized and 
partially hydrolyzed products and are more readily attacked by 
hydrolyzing agents than are the celluloses of group A . 

The fibres of group C are in most cases complex, both struc- 
turally and chemically. They are oxycelluloses and are still 
less resistant than the group B celluloses. They undergo gradual 
oxidation in dry air at a temperature of 100 degs. and become 
discolored. 

In still a fourth group may be classed those cellular, rather 
than fibrous, celluloses which offer low resistance to hydrolysis. 
These are easily resolved by boiling with dilute acids and are 
also soluble to some extent in dilute alkaline solutions. As the 
celluloses of this group are not employed in paper making no 
further discussion of their properties is essential in this work. 

Compound Celluloses. Passing from the consideration of the 
purified celluloses to what may be called their raw materials, it 
is found that plant physiologists recognize three modified or 
"compound" celluloses: cutocellulose, pectocellulose and ligno-. 
cellulose. 

Cutocelluloses contain, mixed with the tissues, various oily 
and waxy substances which render them quite water-resistant. 
The two principal types of these compound celluloses are cork 
and the cuticular tissues of leaves, stems, etc. Cork contains, in 
addition to oils and waxes, tannins, lignocelluloses and nitroge- 
nous materials. No celluloses of this type are employed in 
paper manufacture, hence a knowledge of their properties is only 
of incidental interest. 

The pectocelluloses may be considered either as compounds 
or intimate mixtures of cellulose and colloidal carbohydrates 
which are easily hydrolyzed by either acid or alkaline treat- 
ments to simpler, soluble materials. They are "saturated 
compounds" and therefore do not react with the halogens. Cel- 



24 CELLULOSE 

luloses of this kind are widely distributed in the plant world 
and are extremely varied in composition and structural char- 
acter. Among the more important pectocelluloses are flax and 
such other non-lignified fibres as ramie, hemp, nettle fibres, 
sisal, esparto, bamboo, etc. Many of these are more or less 
associated with lignocelluloses. While many of the pecto- 
celluloses enter into paper making operations, it is not as pecto- 
celluloses, but only after the separation of the pectic constituents 
by means of alkaline hydrolysis. 

Lignocelluloses form by far the most important group of 
compound celluloses, so far as paper making operations are con- 
cerned, both because they are employed directly, as in the case 
of ground wood and jute, and also because they are the basic 
raw materials from which the greater part of the paper making 
celluloses are prepared. They have been studied in consider- 
able detail by Cross and Bevan, who worked on jute fibre, which 
they consider to be the typical lignocellulose. 

One essential feature of lignification is the formation of meth- 
oxyl groups, O • CH 3 , while a second ke tonic grouping, CO • CH 2 , 
is also a characteristic constitutional feature. This latter group 
doubtless plays an important part in the formation of acetic 
acid during hydrolysis. Woods are more pronounced ligno- 
celluloses than jute, having more non-cellulose constituents and 
yielding more methoxyl and furfural. They are still further 
differentiated from jute by their behavior toward cellulose solv- 
ents, since they yield, as a whole, to no process of solution and 
are, moreover, almost totally resistant to the thiocarbonate 
(viscose) reaction. In all but these two characteristics the 
lignocelluloses of jute and wood are very much alike. 

Jute lignocellulose is dissolved by cuprammonium and by 
zinc chloride either in aqueous or acid solution. Hydrolysis 
accompanies the solvent action, so that on precipitation the 
recovery of the lignocellulose is incomplete. 

Alkalis at high temperature attack and dissolve the lignin 
and the less resistant cellulose but at the same time some of the 
more resistant cellulose is also dissolved. The residual cellulose, 



COMPOUND CELLULOSES 25 

in the case of jute, is very similar in composition to the normal 
cellulose. Acids, even in dilute solutions, rapidly disintegrate 
lignocelluloses at temperatures above 60 degs. Caustic soda 
and carbon disulphide dissolve only part of the lignocellulose, 
50 to 75 per cent remaining undissolved but in such a hydrated 
and swollen condition that it has been known to occupy one 
hundred times the volume of the original fibre. This insoluble 
residue reacts with chlorine as does the original fibre. Oxidizing 
agents profoundly attack lignocelluloses with the formation at 
first of acid products and finally, on further oxidation, of carbon 
dioxide and water. 

Because of the difficulty of separating lignin from cellulose 
without causing decomposition or structural changes, its com- 
position is still regarded as uncertain. Klason * assigns to lignin 
the empirical formula C4oH 42 On and believes the evidence goes 
to show that lignin is not in chemical union with the cellulose. 
Cross and Bevan, 2 on the other hand, have concluded " that the 
fibre substance is not merely a mixture of cellulose with non- 
cellulose constituents, but that these are compacted together 
into a homogeneous though complex molecule by bonds of 
union of a strictly atomic character." They submit the follow- 
ing constitutional formula 3 for the lignin (lignone) of the typical 
lignocellulose, as representing its quantitative reactions of chlo- 
rination, resolution by bisulphites, production of acetic acid and 
estimation of methoxyl. 

/ C °\ /°\ /°\ /OH _ 

HC CH-[CH 2 -CO]2-HC CH • CH • CH • CH/ )3 a 

TLC !cO CH3O.HC JcH.OCHa OH CeUuloses 

^CH£ ^CO' 

Lignin has been investigated by Heuser and Skioldebrand 4 

1 Klason: Beitrage zur Kenntniss der chemischen Zusammensetzung des 
Fichtenholzes. 

2 Cross and Bevan: Cellulose, p. 134, London, 1895. 

3 Cross and Bevan : Researches on Cellulose, III, 104. 

4 Heuser and Skioldebrand: Z. angew. Chem., 1919, 32, 41-45. 



26 CELLULOSE 

who prepared it from spruce wood sawdust by hydrolyzing 
with 42 per cent hydrochloric acid. The yield obtained was 
33.12 per cent and the air dry Hgnin contained 9.25 per cent 
moisture and 0.485 per cent ash. It yielded no furfural but 
showed a copper number of 12.90 and a methyl value of 6.77 
per cent. On destructive distillation it gave more charcoal and 
tar and less acetic acid than cotton or wood cellulose. 

Lignin shows a number of color reactions which are of much 
value in detecting the presence of incrusting matters in paper 
or its raw materials. Nitric acid gives a yellowish brown color; 
a solution of aniline sulphate in water stains lignified tissues 
yellow; paranitroaniline in hydrochloric or sulphuric acid solu- 
tion produces a bright yellowish orange color; while an alcoholic 
solution of phloroglucin acidified with hydrochloric acid devel- 
ops an intense rose red or magenta color. This latter reagent 
has been used as a basis for a quantitative method for estimating 
ground wood in papers. 1 Schwalbe, 2 however, states that the color 
reaction with phloroglucin fails in many cases where lignified fibres 
are present and considers that the results should be confirmed 
in every case by Cross and Bevan's chlorination reaction. 

One of the most characteristic reactions of lignin is that of 
direct combination with the halogens, and more especially with 
chlorine. In the presence of water, chlorine attacks lignin with 
the formation of a chloride, C 19 Hi 8 Cl 4 09. This chloride is bright 
yellow in color and is soluble in sodium sulphite solution with 
the production of an intense magenta red color. With jute the 
chlorine combining with the lignin amounts to 8 per cent of 
the lignocellulose and an equal amount is combined as hydro- 
chloric acid; with wood, on the other hand, the proportions are 
not equal, considerably more chlorine going to form hydro- 
chloric acid than corresponds with that which is used in chlo- 
rinating the lignin. This reaction with chlorine is simple and 
there is no indirect oxidation as a result of the reaction CI2 + H 2 
= 2 HC1 + O. The chlorinated material is homogeneous and as 

1 Cross, Bevan and Briggs: Chem. Ztg., 1907, 31, 725. 

2 Schwalbe: Z. angew. Chem., 1918, 31, pp. 50 and 57. 



DETERMINATION OF CELLULOSE 27 

the cellulose is unattacked, maximum yields of the latter are 
obtained. This reaction forms the basis of Cross and Bevan's 
method for the quantitative determination of cellulose. 

Determination of Cellulose. The amount of cellulose in any 
raw material determines the maximum yield of pure fibre which 
can be prepared by any of the chemical processes used in pulp 
making. Practically, however, the yield never reaches this the- 
oretical maximum because of the hydrolytic action of the cook- 
ing liquors and the oxidizing and solvent action of the alkaline 
bleaching agents used. A method for accurately determining 
the cellulose in wood, or any fibrous raw material, is therefore 
of great value to the paper maker, in that it enables him, on the 
one hand, to detect variations in his supplies and, on the other, to 
see how nearly his processes are approaching the optimum. 

A satisfactory method for the determination of cellulose must 
separate it in a form which is free from lignin and colored im- 
purities and which is as- pure as possible. Freedom from min- 
eral matter is of secondary importance since it can be allowed 
for or removed by treatment with dilute acids. The formation 
of oxycellulose and hydrocellulose must especially be guarded 
against since in their formation part of the cellulose is converted 
to soluble products and moreover they are easily attacked by 
many of the reagents- employed. Another consideration is that 
the process should involve no very complicated operations and 
that it should be capable of completion within a reasonably 
short time. 

Many methods for determining cellulose have been proposed, 
of which some do not remove all non-cellulose matter, some 
destroy part of the cellulose itself, and some, which give pure 
products, are too long and complicated for practical work. It 
is unnecessary to give the full details of all the proposed methods, 
but a very brief description may prove of interest to those who 
wish to study into the subject. The following outlines, to- 
gether with notes on the purity of the products, are taken from 
Renker's x work on methods of determining cellulose. 

1 Renker: Uber Bestimmungsmethoden der Cellulose, Berlin, 1910. 



28 CELLULOSE 

Konig * heats 3 grams of the sample with 200 c.c. of glycerine 
(sp. gr. 1.230) and 4 grams of concentrated sulphuric acid. The 
flask is fitted with a reflux condenser and the heating is con- 
tinued for just one hour at the boil (131 to 133 degs.); the 
residue is then washed with hot water, alcohol and ether, dried 
and weighed. This process strongly attacks the cellulose and 
the product is not pure cellulose though entirely free from 
pentosans. 

Cross and Bevan's 2 method depends upon the chlorination 
of the lignin by treating the moist material with chlorine gas 
and the subsequent solution of the chlorinated products by 
boiling with dilute sodium sulphite solution. The cellulose ob- 
tained is pure white and free from lignin, but consists, according 
to the terminology of Cross and Bevan, of a mixture of a and /3 
celluloses, the latter being of low resistance toward hydrolytic 
agents and yielding furfural on boiling with hydrochloric acid. 

Modifications of Cross and Bevan's method in which chlorine 
water is used instead of the gas give lower yields and the product 
contains some oxycellulose. 

In H. Miiller's 3 process the sample, after extraction of the 
resins and boiling in water, is treated with 5 to 10 c.c. of dilute 
bromine water diluted with 100 c.c. of water. When the color 
indicates that the bromine is all used up, more bromine water 
is added until an excess of the reagent remains; this takes from 
12 to 24 hours. The residue is filtered off and washed. This 
process is repeated until the fibrous residue is pure white. This 
process yields highly pure cellulose which is free from oxycel- 
lulose but too long a time is required, especially with woods 
which may require twenty repetitions of the treatment. Kla- 
son's 4 modification, involving preliminary treatment of the 
sample with calcium or magnesium bisulphite solution, gives 
lower yields than Miiller's original method and, although the 

1 Konig: Z. Nahr. Genussm., i, 8 (1898). 

2 Cross and Bevan: Cellulose, 95 (1895). 

3 Hofmanns Ber. iiber die Entwickl. d. chem. Industrie, III, 27 (1877). 

4 5 Internationaler Kongress fiir angewandte Chemie, 1903, 1, 309. 



DETERMINATION OF CELLULOSE 29 

time required is less, the method is still unsatisfactory tech- 
nically. 

The Schulze-Henneberg 1 method consists in digesting the 
sample for 12 to 14 days at 15 C. with 0.8 part KC10 3 and 12 
parts HNO3 (1.10 sp. gr.). This is followed by dilution, filter- 
ing and washing and then by digestion with dilute ammonia for 
45 minutes at 6o° C. The residue is washed with ammonia and 
finally hot water. This process requires an excessive time and 
very careful control of the temperature, and the results obtained 
are low and irregular, especially with woods. 

Hoffmeister 2 treats the sample with hydrochloric acid (1.05 
sp. gr.) and as much potassium chlorate as will dissolve during 
the reaction. The digestion is conducted at ordinary tempera- 
ture, — not over 17.5 C, — with frequent shaking for 24 to 36 
hours or until all parts of the fibre have become a clear yellow. 
The residue is then washed, digested on the water bath for 1 to 2 
hours with dilute ammonia, washed, dried and weighed. This 
process yields a product which is free from lignin but is some- 
what yellow; the cellulose is somewhat attacked and oxy cellu- 
lose is present. 

Digestion at 60 degs. with a large excess of nitric acid (10 
per cent) has been proposed by Cross and Bevan. 3 When the 
fibre has changed to a yellow color it is washed and treated 
with a solution of sodium sulphite. This treatment hydrolyzes 
and dissolves the /3 cellulose and leaves only the more resistant 
a cellulose; this results in low yields as compared with the 
chlorination process. The products are free from lignin but 
contain oxycellulose and apparently also hydrocellulose. 

Lifschutz 4 digests the material for 14 to 16 hours at a tem- 
perature of 45 to 60 degs. with 10 parts of a mixture of 32 per cent 
sulphuric acid, 18 to 20 per cent nitric acid and 48 to 50 per cent 
water. With wood, very low yields are obtained and the prod- 

1 Ann., 146, 130 (1868). 

2 Landw. Jahrb., 17, 240 (1888). 

3 Cellulose, 97 (1895). 

4 Ber., 24, 1188 (1891). 



30 CELLULOSE 

uct forms a brownish horny mass which is free from lignin but 
contains considerable oxycellulose. 

Schwalbe * treats the moist material for several hours with 
gases containing oxides of nitrogen, washes and heats on the 
water bath with a 2 per cent Na 2 S0 3 solution. The cellulose 
thus obtained is free from lignin but contains oxidation products 
and is brownish yellow. The results are very variable when 
woods are analyzed. 

Zeisel and Stritar 2 suspend the sample in dilute nitric acid 
and add a 3 per cent solution of potassium permanganate a 
cubic centimeter at a time until the color persists for half an 
hour; during this treatment cooling and stirring are necessary. 
The manganese salts are removed by SCVwater or NaHS0 3 
and after washing the residue is digested with dilute ammonia. 
It is claimed that hemicelluloses and about 4 per cent of the 
cellulose are dissolved. The method gives low and variable 
results, forms much oxycellulose and is unsatisfactory for woods. 

Neutral permanganate does not remove all the lignin, while 
if it is used with acetic acid the product is free from lignin but 
contains oxycellulose. Permanganate with hydrochloric acid 
works fairly well with cotton, jute and sulphite, but with woods 
the treatment must be many times repeated and the results 
are low. 

Sodium hypochlorite was found to give low results and though 
the product was free from lignin it was very high in oxycellulose. 3 

After a large number of experiments with the different meth- 
ods, Renker concludes that there is no absolutely correct method 
for determining cellulose but that the method of Cross and 
Bevan using chlorine gas is the most satisfactory. Konig and 
Huhn, 4 on the contrary, contend that Cross and Bevan's method 
gives too high results because it fails to remove pentosans and 
hemicelluloses which remain as impurities in the product. They 

1 D.R.P., 204,460. 

2 Ber., 35, 1252 (1902). 

3 Renker: Bestimmungsmethoden der Cellulose, 79. 

4 Z. Farben-Ind., 1911, II, 297 et seq. 



DETERMINATION OF CELLULOSE 



31 



claim that only hydrolysis followed by oxidation can free the 
true cellulose from all impurities. This brings up the question 
of what constitutes pure cellulose, which has never been settled 
beyond dispute and about which there are probably as many 
opinions as there are methods for its determination. 

The results obtained by Renker, in his investigation of the 
different methods for the determination of cellulose, are given in 
the accompanying table. The percentages are based on mate- 
rial free from ash, fat or rosin, and water-soluble substances. 



Method of analysis 



Glycerine-sulphuric acid. — Konig 

Chlorine gas. — Cross and Bevan 

Concentrated chlorine water 

Dilute chlorine water 

Bromine water. — H. Muller 

Bromine water. — Muller- Klason 

Nitric acid and potassium chlorate. — 

Schulze 

Muriatic acid and potassium chlorate. — 

Hoffmeister 

Nitric acid. — Cross and Bevan 

Nitrous acid. — German pat. 204,460 

Nitric-sulphuric acids. — Lifschiitz 

Potassium permanganate and nitric acid. — 

Zeisel and Stritar 

Potassium permanganate, neutral 

Potassium permanganate and acetic acid . . . 
Potassium permanganate and hydrochloric 

acid 

Hydrogen, peroxide 

Sodium hypochlorite 

Phenol. — German pat. 94,467 



Material 



Sulphite 
cellulose 



Per cent 

74-15 
97-9 
97-65 
98.0 

98-i 
96.6 

98.05 

98.25 
97-65 



90.6 

98.5* 
98.25 

97-9 
96.05 
97-4 
9C75 



Jute 



Per cent 



Wood 



Per cent 

55 



43 



35 



Cotton 



Per cent 



* Inapplicable because lignin is not all removed. 

All things considered the Cross and Bevan method, employing 
chlorine gas, is doubtless the best means of determining cellu- 
lose, especially where woods are under consideration, since it 
has been proved by Heuser and Sieber 1 that lignin can be com- 
pletely removed by chlorination without any oxidation of the 

1 Z. angew. Chem., 26 (1913), 801. 



32 CELLULOSE 

cellulose, and because the color produced by sodium sulphite on 
chlorinated lignin is characteristic and forms a good indicator 
to show the degree of purification. If, however, the chlorine is 
allowed to act after the lignin is all removed the cellulose is 
gradually converted to oxycellulose, which is soluble in sodium 
sulphite, and lower yields result. According to one's under- 
standing of pure cellulose it may or may not be advisable to 
accompany this treatment with one of acid hydrolysis. 

Even where Cross and Be van's method has been employed the 
different methods of operation render the figures of different 
observers hardly comparable. The wood must be very finely 
divided and of uniform particles. If coarse pieces are present 
the lignin chloride formed on the surface prevents further pene- 
tration of the gas and long exposure is of little use unless the 
lignin chloride is removed. Variation in the size of the wood 
particles also means that a portion will be over^treated in order 
to insure the complete removal of the lignin from the rest, and 
this results in lower yields. To avoid many of the manipula- 
tive variations Johnsen and Hovey x worked on wood reduced 
to a fine " sawdust" by rasping with a suitable wood rasp, and 
screened to pass an 8o-mesh but not a ioo-mesh sieve. This 
they chlorinated in a Gooch crucible, the small plate of which 
was carefully covered with fine bleached cloth sewn on with 
cotton thread. Their method, which includes a preliminary 
hydrolysis, is in detail as follows: 

Two samples of about one gram each of air dry sawdust are 
weighed exactly, transferred to small flasks and heated for one- 
half hour with alcohol, on a water bath, filtered through the 
crucibles and washed with hot alcohol. The material is then 
transferred from the crucibles to 150 c.c. flasks and covered 
with about 75 c.c. of glycerine-acetic acid mixture (60 grams 
glacial acetic acid and 92 grams glycerine, 1.26 sp. gr.). The 
flasks are then heated in an oil bath at 135 C. for four hours, 
using glass tubes as reflux air condensers. The material is then 
collected in the crucibles, washed well with hot water and the 

1 Pulp and Paper Mag. Can., XVI (1918), 85. 



DETERMINATION OF CELLULOSE 33 

crucibles, after cooling, are placed in an apparatus permitting 
washed chlorine gas to be passed directly through the crucible 
and its contents. After passing chlorine through continuously 
for 20 minutes the free gas is removed by washing once with a 
cold, weak solution of sulphurous acid in water, and the cru- 
cibles are placed in small beakers which are filled not quite to 
the top of the crucibles with a 3 per cent solution of sodium 
sulphite. After the beakers have been heated in a water bath 
for three-quarters of an hour the material in the crucibles is 
washed with hot water, using a filtering flask, and allowed to 
cool. The chlorination process is then repeated three times 
exactly as before except that the duration of gassing is 15, 15 
and 10 minutes. After the last treatment with sodium sulphite 
the fibres are thoroughly washed, dried at 105 C. for four 
hours, or to constant weight, and weighed in closed weighing 
bottles. The moisture in a separate sample of the original 
sawdust having been determined, the per cent of cellulose can 
be calculated over to the basis of bone dry wood. 

Working by this method the lignin may be completely re- 
moved from finely divided wood in four chlorinations totalling 
one hour's exposure to the gas. If the treatment with glycer- 
ine and acetic acid is omitted the results are 2 to 4 per cent 
higher, indicating the extent to which hydrolysis removes sub- 
stances which are not dissolved by the straight chlorination 
process. 



CHAPTER II 
FIBROUS RAW MATERIALS 

The Vegetable Cell. The structural unit of which the plant 
fabric is composed is the cell, and even those elements which 
are least cellular in appearance, as fibres, ducts, etc., are only 
transformed cells, or simple combinations of them. In all of 
the higher forms of plant life the living cell consists essentially 
of protoplasm surrounded by a wall of cellulose. The proto- 
plasm is practically transparent and colorless but it is seldom 
found without an admixture of other matter which gives it a 
granular appearance. Chemically considered it is a very com- 
plex substance belonging to the group of albuminoid bodies 
and is quite similar in composition and appearance to the albu- 
min which forms white of egg. 

The cell wall is produced from the substances contained in 
the protoplasm and is formed in close contact with the limiting 
film of the latter. At first it is an even, homogeneous film 
showing no obvious structure but it soon becomes modified in 
appearance and composition according to its location in the 
plant; in some cases it becomes capable of absorbing a large 
amount of water with a consequent increase in volume and the 
formation, upon warming, of a thick mucilage. In other cases 
it becomes mineralized by the deposition of silica or calcium 
salts upon or within the cell wall, the effect being a hardening 
and stiffening of the structure as illustrated by many of the 
grasses and straws. A third modification of the cell wall is 
known as cutinization or suberification. Ordinary cell walls 
absorb water freely but in certain parts of the plant they are 
water-repellent due to the presence of cutin or suberin. This 
water-proofing of the cell wall may be superficial only or it may 
permeate the entire structure of the wall as in the case of cork. 

34 



THE VEGETABLE CELL 



35 



A fourth change, which, from the point of view of the paper 
maker, is far more important than the others, is known as ligni- 
fication and is caused by the deposition in and upon the cell- 
wall of a substance somewhat similar to cellulose and which is 
termed lignin. This material, although generally spoken of as 
a single substance, is in all probability made up of several 
closely related substances. It forms by far the greater part of 
the incrusting matters which are removed by the treatment 
with chemicals in preparing celluloses for paper making. The 
chemical properties of the lignocelluloses have already been 
described in the preceding chapter. 

The thickening of the cell wall, which up to a certain age 
accompanies the deposition of lignin, seldom takes place uni- 
formly over its entire surface. As a result the fibres may show 
ridges, depressions, pits, rings, spirals and other markings, which 
are often so characteristic as to be of great assistance in the 
identification of the fibres in which they occur. In some cases 
it is easy to see that the markings are pores or fissures running 
from one cell to the next. Such pores and the thinner portions 
of the cell walls aid in the transmission of sap. 

In many plants gums and resins are formed by processes 
which are not well understood but which are probably in large 
part degradations of the cell walls. The products of such 
changes are often found as small, irregular drops either within 
the cells or in the spaces, known as resin ducts, arising from the 
confluence of a number of cells. The resins are soluble in alco- 
hol or in solutions of the alkalis; they are colored reddish orange 
by a solution of Sudan III in diluted alcohol and when stained 
in this way may be readily recognized under the microscope. 

It is only the living cells which contain protoplasm and these 
are found at the points where growth is taking place. The older 
cells, where growth has ceased, occasionally contain a little 
water but generally only air, more or less highly rarefied. They 
are still of value in the plant structure for it is from such lifeless 
cells that stiffness and strength are derived. Cells are present 
in different plants in an almost infinite diversity of form, but, 



$6 FIBROUS RAW MATERIALS 

except for those cases which assist in the identification of the 
fibres which they accompany, the following discussions will be 
confined to the long, slender pointed elements of the bast or 
woody tissues, which, with the single exception of cotton, are 
the only ones of practical interest to the paper maker. Such 
fibres are derived from the ordinary cells simply by growth and 
change of form. 

The paper making fibres may be divided, according to their 
source, into four classes. 

i. Seed hairs, of which cotton is the only representative. 

2. Bast fibres, as hemp, flax, manila, etc. 

3. Those derived from whole stems, such as straw, esparto, 
or bamboo, and which are associated with various cells and 
vessels which are not properly fibres. 

4. Fibres derived from wood. 

Seed Hairs 

Cotton (Gossypium). The cotton fibre consists of a single 
hair-like cell, which when fully ripe is flattened and twisted. 
This appearance is a characteristic of fully matured cotton and 
is not shown by unripe fibre or that which has been injured 
during growth. The fibres form the covering of the cotton 
seed and are removed from the seed by ginning. The length of 
the cotton fibre varies from 2 to 5.6 cm. and the diameter 
from 0.0163 to 0.0215 mm.; the longest fibres are found 
in the Sea Island cottons, followed by Egyptian, Brazilian, 
American and East Indian. The cell walls of the mature cotton 
are thin and often present a granulated appearance, or highly 
characteristic cross-markings. 

Raw cotton has been examined by Schunck who found in it 
two coloring matters, both containing nitrogen; a wax similar 
to carnauba wax; albuminous matter and a solid crystalline 
fatty acid. Miiller has analyzed raw cotton with the following 
results : 



LINEN 37 

Per cent 

Water 7. 00 

Cellulose 91 .35 

Fat o. 40 

Aqueous extract (containing nitrogeneous substances) o. 50 

Ash o. 12 

Cuticular substance (by difference) o. 63 

Cotton reaches the paper mill in the form of rags and spinning 
waste. The short fibres removed from the seed hulls by me- 
chanical processes are also occasionally available and can be 
used in high-class papers. 

Bast Fibres 

Under this heading are included the fibres found in the inner 
bark of various plants. These are often present in the plant 
in the form of bundles of considerable length and it is these 
fibre bundles or filaments which are of particular interest in 
textile work, while the paper maker is concerned only with the 
ultimate fibres composing these filaments. The fibres are usu- 
ally firmly attached to those above and below them, either by 
incrusting matters or by partial identity of their cell walls, so 
that a chemical treatment is generally necessary in separating 
them. The filaments, on the other hand, are isolated from the 
surrounding tissues by various mechanical or chemical processes, 
one of the commonest being retting as applied to flax and hemp. 

The walls of bast fibres are usually of considerable thickness 
and the central canal varies greatly in the different species 
and even in different individuals of the same species. The 
irregularities of the cell walls are such as to cause thickenings 
or knots in some cases, projections into the cell cavity or out- 
ward from the walls, and various other characteristic appear- 
ances. Variations in the amount of lignification and in the 
nature of the materials deposited in and on the cell walls are 
frequently sufficiently characteristic to assist materially in their 
identification. 

Linen. Linen is composed of the bast fibres of the flax plant 
Linum usitatissimum. The plant yields about 8 per cent of 



38 



FIBROUS RAW MATERIALS 



fibre which is separated by retting and is then known as flax. 
The ultimate fibres are 6 to 60 mm. long and 0.012 to 0.026 mm. 
wide with an average ratio of length to width of about 1200. 
They are thick walled tubes with thickened places or knots at 
intervals. The ends are tapered, the walls rather transparent, 
and the canal is small. Miiller gives the analyses of two samples 
of Belgian flax as follows: 





Per cent 


Per cent 


Water 


8.60 
81.99 
2.37 
3.62 
O.70 

2 .72 


10.56 


Cellulose 


7° -55 


Fat and wax 


2-34 




5-94 


Ash 


1 .32 


Pectous substances 


9.29 







Linen or flax reaches the paper mill in the form of scutching 
refuse, spinning waste, threads, rags, etc. It requires much 
the same treatment as given to cotton except that it is necessary 
to employ a rather more severe bleaching process. 

Hemp (Cannabis sativa). The fibre is prepared by retting, 
from filaments which run the entire length of the stem. The 
ultimate fibres composing these filaments vary from 5 to 55 
mm. and average about 22 mm. long by 0.022 mm. in diam- 
eter, the ratio of length to diameter being therefore about 1000. 
The fibres have very thick walls which are not very highly 
lignified. The ends are large and sometimes flattened and the 
central canal is almost obliterated. In microscopic appearance 
the fibres are very similar to those of flax; they show the same 
knots or thickenings and the same striae, but they differ from 
linen in having more ability to break down into fibrillae during 
the mechanical processes of paper making. 

Miiller gives the following as the analysis of a sample of raw 
Italian hemp. 

Per cent 

Water 8.80 

Cellulose 77 • 13 

Fat and Wax 0.55 



JUTE 39 

Per cent 

Aqueous extract 3 . 45 

Ash o. 82 

Pectous substances 9. 25 

Many other plants yield fibres to which the name hemp is 
given but they are generally distinguished as manila hemp, 
sisal hemp, sunn hemp, etc. 

Hemp comes to the paper mill in the shape of rags, rope and 
cordage, etc. It is used in high-grade papers, particularly very 
thin sorts, where its ability to split into fibrillae makes it espe- 
cially valuable. 

Manila Hemp (Musa textilis). Manila is prepared from the 
outer sheath of the stems of the Musa, which is a species of 
banana, by stripping, scraping and drying. It is sometimes 
further purified by washing and beating. 

The ultimate fibres are from 3 to 12 mm. long and average 
about 6 mm.; the width varies from 0.016 to 0.032 mm. with 
an average of 0.024 mm. The fibres taper very gradually 
toward the ends; the central canal is large and very prominent, 
while fine cross-markings are numerous. 

The composition of raw manila is given by Muller as follows: 

Per cent 

Water n. 73 

Cellulose 64. 07 

Fat and wax o. 62 

Aqueous extract o. 96 

Ash 1.02 

Lignin and pectous substances 21. 60 

The paper maker obtains manila fibre almost entirely in the 
form of old ropes and cordage. It is generally given a compara- 
tively light alkaline treatment with lime and used in the un- 
bleached condition for papers where strength is of far more 
importance than cleanliness or color. It is occasionally bleached 
to a light yellowish shade for some grades of paper. 

Jute (Corchorus capsularis and C. olitorius). The filaments 
are obtained by a retting process, and are used in the manu- 
facture of twine, cordage, and woven goods such as burlap. 



40 



FIBROUS RAW MATERIALS 



It is in these forms and also as "butts" and "rejections" that 
it reaches the paper maker. 

The fibres of jute are about 2 mm. long and 0.022 mm. in 
diameter. They are thick- walled and the central canal is very 
variable, at times being of considerable width and then narrow- 
ing to hardly more than a line. The surface is quite smooth 
and at intervals may be noticed radial canals and joints similar 
to those in linen though not so pronounced. As used in paper 
making the fibres are not completely separated, so that bundles 
of fibres are of frequent occurrence. 

Jute has been carefully studied by Cross and Bevan who regard 
it as typical of lignified fibres. They consider it as a chemical 
unity, which they term lignocellulose, and which splits up into 
cellulose and other products on treatment with suitable reagents. 

Muller gives the composition of the raw fibre as follows: 





First quality 


Butts 


Water 


Per cent 
9-86 

63.76 
0.38 
1 .00 
0.68 

24.32 


Per cent 
12 .40 


Cellulose 


60.89 
O.44 
3-89 
1 .40 

20.98 


Fat and wax 


Aqueous extract 


Ash 

Lignin or non-cellulose 





Adansonia (Adansonia digitata). This fibre, which is derived 
from the inner bark of the baobab, or monkey bread tree, of 
Africa, has been used to some extent in preparing papers where 
the very highest strength is a necessity. The composition of 
the bast as exported varies, as shown below: 1 





Per cent 


Per cent 


Water 


10.90 
49-35 

0.94 
13-57 

6.19 

I9-05 


13.18 


Cellulose 


58.82 


Fat and wax 


0.41 


Aqueous extract 


7.08 


Ash 


4.72 


Pectous substances 


15 .19 







Griffin and Little: Chemistry of Paper Making, p. 128. 



FIBRES DERIVED FROM WHOLE STEMS 4 1 

Paper Mulberry Tree {Broussonetia papyrifera). The fibres 
of the paper mulberry are used by the Japanese in the prepara- 
tion of some of their peculiar papers. They are separated 
from the inner bark of the tree by scraping, soaking and mace- 
ration in water, and are sometimes purified still further by 
boiling in weak alkaline solutions. As used in Japanese papers 
the fibres are generally unbroken. 

The fibres are long and slender, varying in length from 6 to 
20 mm., with an average width of 0.030 mm. They are nearly 
transparent when viewed under the microscope, and show trans- 
verse jointings as well as longitudinal striae. The central canal 
generally shows as a well-defined line and the ends are some- 
times blunt and rounded, sometimes fringed. 

Agave. Fibres are prepared from the leaves of various species 
of agave by maceration or scraping. The filaments thus obtained 
are light colored, lustrous and comparatively stiff. Among the 
most common of the fibres of this class is sisal hemp or heniquen, 
which is largely employed for cordage, bags, etc., in which 
forms it reaches the paper mill. 

The ultimate fibres are long, of rather small diameter, taper- 
ing and pointed at the ends. The central canal is not promi- 
nent but can be seen as a narrow line in some of the fibres. The 
walls are thick and are characterized by many fine cross lines, 
close together, which are found on nearly every specimen. The 
fibres are harsher than paper mulberry and longer than manila. 

Fibres Derived from Whole Stems 

The fibres in this class, being produced by treatment of the 
entire stems, include the ultimate fibres from all structural ele- 
ments of the stem proper, together with cells from the epidermis 
and other parts of the plant. 

Straw. In straw pulp the bast cells or fibres form the greater 
part of the pulp. These are comparatively short and slender 
with sharp pointed ends; at quite regular intervals the walls 
appear to be thickened and drawn together to resemble joints. 



4 2 



FIBROUS RAW MATERIALS 



The dimensions of straw fibres vary with the kind of straw and 
with the conditions of growth, nature of soil, etc. They are 
longer than those from esparto but not so long as the fibres 
from spruce wood and would compare more nearly with poplar 
fibre in paper making value. 

Accompanying the bast fibres in straw pulp are numerous 
epidermal cells with toothed or serrated edges, and also smooth, 
thin-walled cells from the pithy portion of the stem. The 
latter vary in shape from nearly round to long, oval cells whose 
length is several times their width. Both types of cell aid 
materially in the identification of straw pulp. 

Esparto {Stipa tenacissima and Lygeum Spartum). The bast 
fibres are grouped in bundles or filaments which are resolved 
into ultimate fibres by the chemical processes employed. The 
fibres are shorter and more even than those from straw, aver- 
aging about 1.5 mm. in length, and the central canal is nearly 
closed. Serrated cells are numerous but considerably smaller 
than those from straw, while the smooth, thin-walled cells are 
absent. The chief characteristic which distinguishes esparto 
from straw and other fibres is the presence of small tear-shaped 
cells derived from the hairs on the surface of the leaves. 

The composition of esparto is given by Miiller as follows : 





Spanish 


African 


Water 


Per cent 

9-38 
48.25 

2 .07 
IO.19 

3-72 
26.39 


Per cent 
8.80 


Cellulose 

Fat and wax 

Aqueous extract 

Ash 

Pectous substances 


34.80 
2.62 
9.81 

3-67 
29.30 





Cross and Be van 1 give the percentage of cellulose in air dry 
esparto as follows: Percent 

Spanish 58. o 

Tripoli 46. 3 

52.0 

45-6 

1 Cross and Bevan: Text Book of Paper Making. 



Arzew. 
Oran. . 



BAGASSE AND CORN STALKS 43 

Bamboo. Bamboo fibres closely resemble those from the 
straws in many of their characteristics. According to Raitt 1 
the average length of the ultimate fibres is from 2.20 mm. to 
2.60 mm. according to the variety, and the diameters are from 
0.018 to 0.027 mm. While not so long as spruce fibres they 
are much longer than those from any of the deciduous trees. 
Accompanying the true fibres are numerous serrated cells and 
ovoid pith cells of various sizes and shapes. Cells similar to 
the tear-shaped cells of esparto have also been noticed. Many 
of these different cells are very small and a good proportion of 
them would be lost during the preparation of the pulp. 

The number of species of bamboo runs into the hundreds 
and not all of them are suited for paper making work because 
of the difficulties in reduction to pulp and bleaching to good 
color. 

Rushes. In many districts there are large areas of swamp- 
land densely covered with rushes of various kinds. Investi- 
gation has shown that the fibres in these are very similar to 
esparto and that pith cells are also present though they are far 
smaller than those from straw and many would be lost during 
the washing and bleaching of the fibre. 

Examination of rushes from South Carolina showed that they 
contained 35 per cent of cellulose and that of this about 30 
per cent consisted of fine pith cells which would wash easily 
through a 100-mesh sieve. 

Rushes appear to require a more drastic cooking treatment 
than straw or esparto and the fibres bleach a little harder. They 
are, however, potential sources of fibre which can be availed of 
when necessity arises. 

Bagasse and Corn Stalks. These two materials are so similar 
in their fibrous characteristics and in the treatment necessary 
in cooking them that they may be considered as practically 
identical. Bagasse, the crushed stalks of the sugar cane, is 
produced in large quantities in the sugar industry and is gen- 
erally burned as fuel, though its value for this purpose is com- 

1 Raitt: Indian Forest Records, Vol. Ill, Part III. 



44 FIBROUS RAW MATERIALS 

paratively low because of its wet condition. It is estimated 
that seven States in the "corn belt" produce annually about 
eighty million tons of corn stalks of which the greater part is 
practically a waste. 

Both of these materials can be reduced to a pulp quite easily 
by the soda process and the pulp will bleach to a good white 
color with less than 10 per cent of bleach. The ash in the stalks 
is considerably lower than that in straw and contains much less 
silica, so that its effect on the recovery process is very slight. 

The pulp from both raw materials consists of long thick- 
walled fibres mixed with shorter fibres of similar structure and 
cells of various shapes and sizes. These include serrated cells 
of comparatively large size, long thick cells with rounded ends 
and many pith cells which are so thin-walled that nearly all 
become flattened during the reduction process. These pith cells 
are much larger than those from straw and are therefore much 
more difficult to remove by washing. They impart to the paper 
made from this fibre a hardness and rattle which are undesirable 
in many products, and as their separation from the rest of the 
fibre has proved very difficult the presence of pith has proved 
one of the chief stumbling blocks in the way of using either 
bagasse or corn stalks. 

Miscellaneous Materials. Among the many substances pro- 
posed as sources of fibre the following may be considered as 
falling in this class: papyrus x which grows in immense quanti- 
ties along the Nile and which yields about 33 per cent of easy- 
bleaching pulp when cooked by the soda process; asparagus 2 
waste from canning factories and dry stalks at the end of the 
season; pea and bean vines 3 which according to Reinke yield 
better fibre than asparagus; cotton stalks, of which immense 
quantities are burned every year, but which so far have never 
been utilized successfully; zacaton, a Mexican grass, which 
has been carefully investigated by the Bureau of Plant Indus- 

1 Beam: Chem. Section Bull. No. 2, Welcome Tropical Research Lab. Sudan. 

2 Reinke: Chem. Ztg., 19 13, 37, 81. 

3 Reinke: J. Soc. Chem. Ind., 1913, 594. 



woods 45 

try; x tropical grasses, numerous species of which have been 
tried on an experimental scale by Raitt, 2 Richmond 3 and others. 
Many of these have been found to produce excellent fibre. 

Peat also might possibly be considered in this class. Numer- 
ous attempts have been made to produce useful fibre from peat, 
the treatments given ranging from an entirely mechanical pro- 
cess, through treatment with alkalis and acids, to fermentation 
processes. All methods have thus far failed to produce a fibre 
which can be used in anything but the coarsest products. 

Woods 

The woody tissues of plants are made up of cells which exhibit 
great diversity of form, size, and markings as the accompanying 
drawings Figs, i and 2 show. Those in which the paper maker 
is particularly interested are the true wood fibres, or libriform 
cells, and the tracheids, but many of the other cells are of inci- 
dental interest as helping to identify the wood from which they 
were derived. 

The wood fibres are always spindle or fibre-form and the walls 
are relatively strongly thickened. They never have true spiral 
striations; in only a few species do they show pits, which are 
generally elongated and oblique. Wood fibres are variable in 
length in different woods, ranging from 2.0 mm. to 0.14 mm., 
but in all cases they are the longest elements present. As an 
example of wood fibres may be cited the chemical pulp made 
from poplar wood; this contains in addition only the ducts and 
rarely a few of the small cells from the medullary rays. 

Tracheids are elongated and tapering cells, more or less ligni- 
fied and having peculiar markings known as bordered pits or 
discoid markings. Fig. 3 shows these as they appear on the 
surface of the fibre and illustrates how they are formed by the 
thin partition wall between two tracheids. These pits are so 
constant in number and mode of distribution that they may be 

1 Brand and Merrill: Bull. No. 309, U. S. Dept. of Agriculture. 

2 Raitt: Indian Forest Records, Vol. V, Part III. 

3 Richmond: Philippine J. Sci., 1906, 1, 433-462. 



4 6 



FIBROUS RAW MATERIALS 




Fig. i Drawings of Wood-elements 

1-7. Avicennia sp. 1. Wood-parenchyma cells; tangential section. 2. Sep- 
tum of a duct. 3, 4, 5. Conjugate wood-parenchyma cells. 6, 7. Portions of 
spirally striated libriform fibres. 8-1 1. Bast cells of Cytisus laburnum. 8. 
Cross-section through young bast bundle acted on by chloroiodide of zinc. 9, 10, 
n. Cross-sections through young bast cells similarly treated. 12. Porlieria 
hygrometrica; radial section of conjugate substitute fibres. 13. Jatropha mani- 
hot, radial section through wood. 14-18. Tectona grandis; elements separated 
by maceration. 14. Conjugate wood-parenchyma cells. 15. Ordinary wood- 
parenchyma fibre. 16. Substitute fibre. 17. Libriform fibre. 18. Septate libri- 
form fibre. 



WOODS 



47 




Fig. 2. Drawings of Wood-elements 

19. TracheidfromTectonagrandis. 20-23. Porlieria hygrometrica. 20. Con- 
jugate substitute fibres in cross section. 21. Ordinary substitute fibre after 
maceration. 22, 23. Conjugate substitute fibres after maceration. 24-27. Cy- 
tisus laburnum; elements after maceration. 24. Wood-parenchyma fibre. 25. 
Tracheid. 26. Substitute fibre. 27. Simple libriform fibre. 28. Cross-section 
through cambium and youngest wood of Cytisus laburnum. 29, 30. Mahonia 
aquifolium; ducts. 29. After maceration. 30. Longitudinal section. 31-36. 
Extremeties of ducts separated by maceration from Hieracium. 37-39. Ducts 
from Onopordon acanthium. 40. Spirally marked duct from Vitis vinif era. 41. 
Libriform fibre from Jatropha manihot. 



48 



FIBROUS RAW MATERIALS 




Fig. 3. Discoid Markings on Wood Cells 

Pinus laricio; a. Radial walls"; b. A transverse section. 

Pinus sylvestris; c. Development of markings; d, e. Transverse sections of 
nearly perfect and perfect discoid markings. 



used as a distinguishing characteristic for some woods. In 
cone-bearing or coniferous trees, such as spruce, fir, hemlock, 
etc., the wood consists almost entirely of tracheids, and when 
sulphite fibre or ground wood from such trees is examined under 
the microscope the discoid markings may be very readily seen. 
These tracheids are generally much longer than the libriform 



FIBRE LENGTH 49 

fibres from other woods and hence possess greater paper making 
value. 

Sap and Heartwood. The sapwood, or that of compara- 
tively recent growth, is usually lighter in color and contains 
more fermentable material than the older and denser heart- 
wood. Each year a layer of sapwood goes over into heartwood 
which becomes darker and harder from infiltration of coloring 
matters, resins, etc. The sapwood is generally preferred for 
pulp because it is more easily reduced by either the mechanical 
or chemical processes. In some woods, as fir and buckeye, the 
difference in color and hardness between heartwood and sap- 
wood is not in evidence. 

Fibre Length. The length of the fibres or tracheids in a given 
tree is known to vary with the position from which the sample 
was taken. This has been very carefully investigated for conif- 
erous woods by Mell, 1 who finds that the length of tracheids 
varies considerably not only in different parts of the same tree, 
but also within the same annual ring at the same distance above 
the ground. In both trunk and branches the average length 
increases from the center outward until the tree reaches its 
maximum height growth, after which it remains quite constant. 
The highest average length of tracheids in the branches is usu- 
ally less than in the trunk. Tracheids also vary in length 
according to the character of the soil and the amount of mois- 
ture, those from trees growing in rich, moist soil being longer 
than those from trees grown in dry soil. Lee and Smith 2 have 
also made very careful studies along similar lines of one or two 
trees of Douglas spruce. Their observations are in general 
confirmatory of those of Mell, though in some respects their 
conclusions are different. 

Because of these variable factors it is very difficult to determine 
the average length of tracheids or of the libriform cells of broad- 
leaved woods. The following table by Mell gives the length of 
tracheids of many of the coniferous woods of the United States; 

1 Mell, Paper Trade J., June 15, 191 1. 

2 Forestry Quarterly, Dec, 1916. 



5° 



FIBROUS RAW MATERIAL 



the figures are the averages of many measurements of samples 
taken from different parts of the trunks and branches. 



Names of trees 



Amabilis fir (Abies amabilis) 

Balsam fir (Abies balsamea) 

White fir (Abies concolor) 

Lowland fir (Abies grandis) 

Alpine fir (Abies lasiocarpa) 

Noble fir (Abies nobilis) 

Port Orford cedar (Chamaecyparis lawsoniana) 
Yellow cedar (Chamaecyparis nootkatensis) . . . . 

White cedar (Chamaecyparis thyoides) 

Western larch (Larix occidentalis) 

Incense cedar (Libocedrus decurrens) 

White spruce (Picea canadensis) 

Engelmann spruce (Picea engelmanni) 

Black spruce (Picea mariana) 

Red spruce (Picea rubens) 

Sitka spruce (Picea sitchensis) 

Knobcone pine (Pinus attenuata) 

Sand pine (Pinus clausa) 

Jack pine (Pinus divaricata) 

Shortleaf pine (Pinus echinata) 

Pifion (Pinus edulis) 

Limber pine (Pinus flexilis) 

Spruce pine (Pinus glabra) • 

Sugar pine (Pinus lambertiana) 

Silver pine (Pinus monticola) 

Lodgepole pine (Pinus murrayana) 

Longleaf pine (Pinus palustris) 

Western yellow pine (Pinus ponder osa) 

f Western yellow pine (Pinus ponder osa) 

Parry pifion (Pinus quadrifolia) 

Red pine (Pinus resinosa) 

Pitch pine (Pinus rigida) 

Pond pine (Pinus serotina) 

White pine (Pinus strobus) 

Loblolly pine (Pinus taeda) 

Scrub pine (Pinus virginiana) 

Red fir (Pseudotsuga taxifolia) 

Redwood (Sequoia sempervirens) 

Bigtree (Sequoia washingtoniana) 

Bald cypress (Taxodium distichum) 

Arborvitae (Thuja occidentalis) 

Western red cedar (Thuja plicata) 

Hemlock (Tsuga canadensis) 

Western hemlock (Tsuga heterophylla) 



Length of fibres 


Mm.* 


Mm. 


Mm. 


aver. 


Max. 


Min. 


3-ii 


5.62 


1,49 


3.10 


4 


21 


1.98 


4-63 


6 


03 


2-73 


4.14 


5 


70 


2.89 


3.16 


4 


13 


2 .07 


4.02 


4 


96 


2.b 4 


3- 6 3 


4 


38 


2.56 


2.47 


3 


02 


i-93 


2 .10 


2 


81 


i-43 


2-59 


3 


80 


i-73 


4.01 


4 


7i 


2.97 


3-53 


4 


21 


2.31 


5-7i 


6 


94 


3.06 


3-48 


4 


13 


2.89 


2-97 


3 


63 


2.48 


2.87 


3 


72 


2.31 


2 .06 


2 


40 


1 .24 


2.85 


4 


38 


1.32 


5.06 


6 


53 


3-72 


5-«9 


7 


19 


4.38 


1 .96 


2 


56 


1.49 


2.94 


3 


9b 


1 .90 


4i3 


5 


45 


2-73 


4-47 


S 


8b 


2-73 


4-39 


5 


45 


2-73 


2.63 


3 


72 


1.82 


5-53 


6 


69 


2.97 


3-3 2 


3 


9 b 


2.48 


2-35 


3 


3° 


1 .40 


2 .10 


2 


89 


1.49 


4 03 


4 


79 


3.22 


3-86 


4 


7i 


2.48 


4.20 


6 


36 


2.64 


3-53 


4 


54 


3.22 


3.10 


3 


88 


2.56 


2-73 


3 


9 b 


i-73 


2.68 


3 


3° 


1.82 


6.99 


9 


25 


4-05 


4.82 


5 


95 


3-47 


4.69 


S 


78 


3-£>3 


2 .02 


2 


39 


i-39 


3-87 


4 


54 


3-i4 


4.01 


5 


04 


2.81 


3 -04 


3 


<>3 


i-73 



* A millimetre is equal to about one-twenty-fifth of an inch, 
t From a tree growing in dry soil. 



MOISTURE IN WOOD 



51 



Among broad-leaved woods the following have been exam- 
ined by the author. The measurements are for the true wood 
fibres and the samples were prepared from wood of commercial 
size. All measurements are in milhmetres. 



Wood 


Length 


Width 


Max. 


Min. 


Avg. 


Max. 


Min. 


Avg. 


Beech (Fagus atropunicea) 

Poplar (Populus grandidentata) .... 

Aspen {Populus tremuloides) 

Cotton gum (Nyssa aquatica) 

Red alder {Alnus oregona) 

Sycamore {Platanus occidentalis) . . 

Red maple {Acer rubrum) 

Buckeye (Aesculus flava) 

Cucumber tree {Magnolia acuminata) 

Umbrella {Magnolia fraseri) 

Tulip tree {Liriodendron tulipifera) 
Sweet gum {Liquidamber styraciflua) 

Black gum {Nyssa sylvatica) 

Elm ( Ulmus americana) • 

Birch {Betula papyrifera) 


1 .72 
1 .62 
1.68 
2.67 
1.77 
2 .21 
1. 19 
0.92 
1.30 
i-47 

1 59 

2 .02 
2.32 
r.98 
1.63 


O.70 
O.71 
O.78 
I .24 
O.84 

0.94 
O.67 
O.46 

0.55 
O.62 
O.64 
O.96 
1. 18 
I.03 
O.78 


1. 13 

1.08 

i-i5 

1.85 
1.23 

i-57 
o.93 
0.62 
0.86 
1.08 

1. 14 

i-55 
1.68 

i-35 
1. 17 


0.029 
0.044 
0.046 

O.IOO 

0.038 
0.033 
0.028 
0.026 
0.036 
0.041 
0.035 
0.036 
0-035 
0.021 
0.042 


0.015 
0.020 
0.020 
0.028 
0.014 
0.016 
0.014 
0.014 
O.020 
0.013 
0.021 
0.022 
0.015 
0.014 
0.014 


0.022 
0.028 
0.032 
0.066 
0.027 
0.024 
O.020 
0.020 
0.029 
0.027 
0.029 
0.031 
0.026 
0.019 
0.025 



Moisture in Wood. The cell cavities of all wood contain 
large amounts of air and moisture. According to Sachs the 
volume percentage of freshly cut fir wood is 

Per cent 

Cell walls 24. 81 

Water 58. 63 

Air cavities 16. 56 

The moisture in wood varies with the amount of seasoning 
it has had and also with the kind of wood, the position in the 
tree, and the time of cutting. Certain kinds of wood in the 
living tree, as for example, white ash, black locust and the 
white and red cedars are comparatively dry; black ash and the 
oaks have about twice as much, and chestnut and buckeye 
about three times as much moisture as white ash; cypress and 
white fir also contain large amounts of water. In the hard 
woods the variation in moisture with the different positions in 



52 



FIBROUS RAW MATERIAL 



the tree is comparatively slight while the conifers show wide 
variations, the heartwood generally being very dry and the 
sapwood very' wet. 

Seasoning greatly reduces the amount of moisture present in 
wood but the rate of drying is not the same for all varieties, 
some losing moisture in one-tenth the time required by others. 
The term "air dry," therefore, is one which may denote almost 
any condition of moisture from 40 per cent down to 4 per cent 
of the total weight, according to the length of seasoning and the 
conditions to which exposed. 

Weight per Cubic Foot. The figure for weight per cubic foot 
is one which is closely connected with the moisture content, 
since the shrinkage in volume due to loss of moisture is not at all 
proportional to the amount of such loss. For this reason it 
is best to base the weight per cubic foot on the absolutely dry 
material. Determinations made by the Forest Service 1 for a 
number of American woods gave the following results : 



Kind of wood 



Balsam fir 

Red fir 

White fir 

Alpine fir 

Lowland fir 

Eastern hemlock 

Western hemlock 

Tamarack 

Lodgepole pine, Montana. . 
Lodgepole pine, California 



Pounds 

per cubic 

foot (bone 

dry) 



21.50 
22.25 
21 .40 
22.00 

21-53 
24.60 
24.80 
32 .00 

25-15 

23 . 20 



Kind of wood 



Jack pine 

Loblolly pine, fall cut 

White pine 

Engelmann spruce, Montana 
Engelmann spruce, Colorado 

Sitka spruce 

White spruce 

White birch 

Poplar 

Black gum 



Pounds 

per cubic 

foot (bone 

dry) 



24.00 
28.86 
20.25 
24.40 
21 .28 
23 .60 
26.4O 
34.20 
24.16 
30-36 



The following table of weights per cubic foot is also from 
data supplied by the Forest Service. In this case the weights 
are for kiln dried material and the bone dry weights would 
probably be about 4 per cent less. This table shows the varia- 
tions which may be expected in wood of the same species when 
grown in different localities and under different conditions. It 

1 The Log of the Lab., Dec, 1916. 



RESINS 



53 



illustrates the impossibility of establishing a figure for any wood 
which will apply in all cases. 



Kind of wood 


Locality 


Pounds per 
cubic foot 
(kiln dry) 


Cypress, bald 


Louisiana 


33 
30-35 
38-42 

32 
28 


Douglas fir 


California, Oregon, Washington. 
Florida, Mississippi 


Longleaf pine 




Wisconsin 


Spruce, red 

Spruce, white 

Red alder 


New Hampshire 


New Hampshire, Wisconsin 

Washington 


25-29 
27 
26 


Aspen 

Basswood 


Wisconsin 


Wisconsin, Pennsylvania 

Pennsylvania, Indiana 


24-26 
41-43 

37 

24 

29 

35 
34-37 

32 
41-42 

34-35 

27 
35 


Beech 




Wisconsin 


Buckeye 

Chestnut 


Tennessee 


Maryland 


Black gum 


Tennessee 

Pennsylvania, Wisconsin 

Wisconsin 


Red maple 

Silver maple 

Sugar maple 


Indiana, Pennsylvania 


Sycamore 


Indiana, Tennessee 


Tulip tree 


Tennessee 


Tupelo 


Louisiana 





Resins. Many woods contain small amounts of volatile oils 
generally approaching terpene (CioHi 6 ) in chemical composition. 
Practically nothing is known regarding their formation. From 
these by oxidation are formed balsams and resins, the former 
being regarded as mixtures of resins with volatile oils. There 
are also in some cases resins which contain gum or mucilage 
and are hence termed gum resins. 

The amount of resin in wood varies greatly with the different 
kinds and with the solvent used in its determination. With 
Canadian woods Richter x obtained the following results : 



Fresh balsam. 
Fresh spruce . 



Ether extract 



Per cent 
0.45-0.85 
0.70-1 .80 



Alcohol extract 



Per cent 

I-I5-3-65 
o . 70-1 . 94 



1 Richter: Wochbl. Papierfabr., 44 (19 13), 4507. 



54 



FIBROUS RAW MATERIAL 



Examination of the resins obtained gave the following con- 
stants : 





Ether resin 


Alcohol resin 




Acid number 


Saponification 
number 


Acid number 


Saponification 
number 


White spruce 


61 
66 


80 
no 


54 
35 


83 
168 


Black spruce 







Richter claims that storage of the wood decreases the ether 
extract and increases the alcohol extract, while Schwalbe and 
Grimm 1 state that seasoning or passing air over the chips reduces 
both ether and alcohol soluble material. 

The ether extract is usually lighter in color and more liquid 
and sticky than the alcohol extract. Part of each is soluble in 
petroleum ether and according to Johnsen 2 it is this portion 
which is responsible in large part for the trouble with pitch in 
sulphite pulp. The portion soluble in petroleum ether is a 
thick yellow liquid and appears to be of a fatty rather than a 
resinous nature; the insoluble part is brown and brittle. 

The resin in Bohemian pine and its distribution in the sulphite 
cellulose made from it have been studied by Sieber, 3 who found 
that cooking removed 4.2 per cent; the knotter, screens, sand 
traps, etc., took out 51.8 per cent, while bleaching removed 
15 per cent. 

Proximate Analysis of Wood. The following table gives the 
analysis of a number of European woods. 4 

1 Schwalbe and Grimm: Wochbl. Papierfabr., 44.(1913), 3247. 

2 Johnsen: Pulp and Paper Mag. Can., 1917, 577. 

3 Papierfabr., 19 15, June 18. 

4 Miiller: Die Pflanzenfaser. 



BARK AND KNOTS 



55 



Wood 



Black poplar 
Silver fir. . . 

Birch 

Willow 

Scotch pine. 
Chestnut . . . 

Linden 

Beech 



Water 


Soluble in 
water 


12 .IO 


2.88 


13-87 


1 .26 


12.48 


2.65 


11.66 


2.65 


12.87 


4-05 


12.03 


S-4i 


10.10 


3-56 


12.57 


2 .41 



Soluble in 

alcohol and 

benzine 



i-37 
o.97 
1. 14 
1.23 
1.63 
1 .10 

3-93 
0.41 



Cellulose 


62 .77 


56 


99 


55 


52 


55 


72 


53 


27 


52 


64 


53 


09 


45 


47 



Incrusting 
matter 



26.91 
28.21 

28.74 
28.18 
28.82 
29.32 
39-14 



Still more complete analyses of seven American woods are 
given by Schorger, 1 all percentages being based on oven dry 
samples. Some of his results follow: 



Wood 



Longleaf pine (Pinus palustris). 

Douglas fir (Pseudotsnga taxi- 
folia) 

Western larch (Larix occiden- 
talis) 

White spruce {Picea canadensis) 

Basswood (Tilia americana) 

Yellow birch (Betula hitea) . . . . 

Sugar maple (Acer saccharum). . 



°-37 
0.38 

0.23 
0.31 
0.86 
0.52 
0.44 



Solubility of wood 



M S 



7-15 
6.50 

12-59 
2 .14 
4.07 

3-97 
•4-36 



a 



6.32 
1 .02 



°o 



&3 



22 .36 
16. 11 

22 .14 

"•57 
23.76 

19-85 
17.64 



< 



0.76 

1 .04 

0.71 
i-59 
5-79 
4-3o 
4.46 



5-o5 
4-95 



7.46 

6.02 

10.80 
10.39 

19-93 
24.63 
21 .71 



58.48 

61.47 

57-8o 
61.85 
61 .24 
61.31 
60.78 



The percentages of cellulose given in this table by Schorger 
are considerably higher than the figures of most other analysts 
for the same, or similar, woods. They are doubtless more accu- 
rate because of the greater pains taken with the work and 
because of the more complete knowledge of the precautions 
necessary to prevent hydrolysis of the cellulose and its conse- 
quent loss during the analytical procedure. 

Bark and Knots. The bark serves as a protective envelope 
for the stem and gradually increases in thickness, as a layer is 
added each year. It contains long bast fibres which give strength 

1 Schorger: J. Ind. and Eng. Chem., 1917, 9, 556. 



56 FIBROUS RAW MATERIAL 

to the bark, and cork cells which, because of their impermea- 
bility, are admirably suited to form a protective covering for 
the tissues beneath. Bark often contains coloring matters and 
tannins, sometimes in sufficient amounts to make extraction 
profitable. It is only slightly acted upon by the chemical pro- 
cesses of pulp manufacture and for this reason is of interest to 
the paper maker chiefly because of the necessity for its removal. 
Recent experiments have led to its use on a small scale as a 
substitute for better grades of material in making roofing felts 
and similar products and it will probably eventually be quite 
fully utilized. 

The loss in barking varies greatly with the size and shape of 
the logs, with the care used by the men in charge of the bark- 
ers, and with the type of barker used. With disc barkers it 
may amount to 10 to 25 per cent of the rough wood. 

Knots are formed at the points where the branches make out 
from the stem or trunk. They are usually very hard and dense 
and are frequently highly charged with resins and coloring 
matters. They are partially reduced by the soda process but 
are almost unaffected by the sulphite process which usually 
fails even to soften them. 

Decay. The importance of decay is becoming greater every 
year because of the increasing cost of wood. Not only does the 
wood stored in the yard decay but ground wood stored in laps 
also suffers damage which is estimated by the Forest Service 
to amount to between five and fifteen million dollars a year. 
The decay of wood stored in piles depends on the size and form 
of the pile, upon temperature and humidity and upon the foun- 
dation upon which the pile is built. Small piles of evenly 
stacked wood will nOt decay because they are well ventilated 
and dry out readily. Neither will the wood in the interior of 
large piles because it is too wet; but between these two ex- 
tremes is a condition where the moisture is just right and the 
fungi flourish wonderfully. The summer, with its high tem- 
peratures, is the time when most of the decay takes place and 
practically no loss is suffered in winter. 



The following photomicrographs show the characteristic forms and markings of a 
number of the typical paper-making fibres. These photomicrographs, as well as 
those in Chapter X, were prepared by the Paper Section of the Bureau of Standards. 




:■ 



I 



Plate i 

Cotton (Gossypium) Magnification ioo diameters. Photographed by 
Bureau of Standards. 




Plate 2 

Linen (Linum usitatissimum) Magnification 100 diameters. Photographed by 
Bureau of Standards. 




Plate 3 

Hemp (Cannabis saliva) Magnification 100 diameters. Photographed by 
Bureau of Standards. 




Plate 4 

Manila (Musa textilis) Magnification 100 diameters. Photographed by 
Bureau of Standards. 




Plate 5 

Jute (Corchorus capsularis) Magnification 100 diameters. Photographed by 
Bureau of Standards. 




Plate 6 

Paper Mulberry (Broussonetia papyrifera) Magnification ioo diameters. 
Photographed by Bureau of Standards, 




Plate 7 

Sisal (Agave rigida) Magnification 100 diameters. Photographed by 

Bureau of Standards. 




Plate 8 

Rice Straw (Oryza sativa) Magnification ioo diameters. Photographed by 
Bureau of Standards. 




Plate 9 
Esparto {Stipe tenacissima) Magnification xoo diameters. Photographed 
Bureau of Standards. 



by 




Plate io 

Bamboo {Bambusa arnndinacea) Magnification ioo diameters. Photographed by 
Bureau of Standards. 




Plate ii 

Corn (Zea mays) Magnification ioo diameters. Photographed by 
Bureau of Standards. 




Plate 12 
Red Spruce (Picea rubens) Magnification 100 diameters. Photographed by- 
Bureau of Standards. 




Plate 13 

Spruce Ground Wood (Picea canadensis) Magnification 100 diameters. 
Photographed by Bureau of Standards. 




Plate 14 

Balsam Fir (Abies balsamea) Magnification 100 diameters. Photographed by 
Bureau of Standards. 




Plate 15 

Jack Pine (Pinus divaricata) Magnification 100 diameters. Photographed by- 
Bureau of Standards. 




Plate 16 

Hemlock (Tsuga canadensis) Magnification ioo diameters. Photographed by- 
Bureau of Standards. 




Plate 17 

Douglas Spruce (Pseudotsnga taxifolia) Magnification 100 diameters. 

Photographed by Bureau of Standards. 




Plate 18 

Aspen (Populus tremnloides) Magnification ioo diameters. Photographed by- 
Bureau of Standards. 




Plate 19 

Yellow Birch {Betula luted) Magnification 100 diameters. Photographed by 

Bureau of Standards. 




Plate 20 

Beech (Fagus atropunicea) Magnification 100 diameters. Photographed by 
Bureau of Standards. 




Plate 21 

Chestnut (Castanea dentata) Magnification 100 diameters. Photographed by 

Bureau of Standards. 




Plate 22 

Tulip-tree (Liriodendron tiflipifera) Magnification 100 diameters. Photographed by 

Bureau of Standards. 




Plate 23 

Sweet Gum (Liquidambar styraciflna) Magnification 100 diameters. 
Photographed by Bureau of Standards. 



V \ 




Plate 24 

Hard or Sugar Maple (Acer saccharum) Magnification 100 diameters. 
Photographed by Bureau of Standards. 




Plate 25 

Soft or Silver Maple (Acer saccharinum) Magnification 100 diameters. 
Photographed by Bureau of Standards. 




Plate 2b 

Black Gum (Nyssa sylvatica) Magnification ioo diameters. Photographed by 
Bureau of Standards. 



KINDS OF WOOD 57 

The actual loss of the wood itself is not the only serious 
feature, for the handling of such materials is expensive because 
of the labor required to cut out the decayed portions. As it is 
never possible to make a complete separation some poor wood 
gets into the digester, cutting down its capacity, injuring the 
quality of the pulp, and using up the cooking liquors uselessly. 
Another serious feature is the fire risk involved by the tinder- 
like decayed portions. It takes but a spark to ignite such 
material and it is said to be responsible for most of the serious 
pulp wood fires. 

The decay in wood yards can be greatly lessened by making 
small piles which will dry rapidly and by piling the wood on a 
foundation of crushed stone or gravel rather than on sod-land. 
Spraying the foundation with a disinfectant is also recommended 
by Haas. 1 Another point is the careful removal of old bark, 
decayed wood and the like; such materials should never be 
left to be covered by new wood. 

Kinds of Wood. The woods most generally employed in the 
United States for the manufacture of both ground wood and 
chemical fibre are spruce and poplar, but the growing scarcity 
of these two species has led to the use of many other kinds. 
The quantities of such other woods depend on the factors of 
price, length of fibre, ease of reduction and the relative loca- 
tions of the mill and the source of the wood supply. The 
questions of length of fibre and weight per cubic foot have 
already been treated and we shall now consider briefly some of 
the woods which are in actual use or which have been tried out 
sufficiently on an experimental scale to demonstrate their value. 
The names and ranges of the various species have been taken 
from Sudworth's " Check List of the Forest Trees of the United 
States," while the other data have been collected from widely 
scattered sources. The species mentioned comprise only a por- 
tion of those which will probably be found suitable for the 
manufacture of paper or pulp in some of its forms. 

1 Haas: J. Soc. Chem. Ind., 1910, 29, 415. 



58 FIBROUS RAW MATERIAL 

Spruces. Red spruce, Picea rubens, ranging from Nova 
Scotia to North Carolina and Tennessee, and white spruce, Picea 
canadensis, are the common pulp woods of the East. The range 
of the latter is from Newfoundland to Hudson Bay, and north- 
westward to Alaska; southward to Northern New York, Michi- 
gan, Wisconsin, Minnesota, South Dakota, Montana and British 
Columbia. Both woods are light, soft, straight grained and 
fairly free from resin. Very similar in quality are Engelmann 
spruce, Picea engelmanni, ranging from northern Arizona through 
the Rocky Mountain region to British Columbia, and Sitka spruce, 
Picea sitchensis, extending on the coast region from Alaska to 
northern California. This latter species is said to be the best 
pulp wood on the Pacific coast. 

All the spruces are reduced easily by the sulphite or sulphate 
process but with considerably more difficulty by the soda pro- 
cess. The soda fibre is very hard to bleach. Because of the 
uniformly light color of the wood all are admirably adapted for 
the preparation of ground wood, Sitka spruce, however, being 
somewhat inferior to the others in color. 

Firs. Balsam fir, Abies balsamea, occurs from Newfoundland 
and Labrador westward to the region of Great Bear Lake and 
southward to Pennsylvania. 

Its wood is very light, soft, not strong, rather coarse grained, 
and not durable. It is frequently cut and used with spruce, 
sometimes to the extent of 20 per cent or more, in the manu- 
facture of sulphite. The fibre is considered somewhat inferior 
to that from spruce and is likely to contain more pitch. Bal- 
sam fir can be successfully used in the preparation of ground 
wood of good color but its use is not favored because of the 
low yield per cord and its tendency to decay. 

Other firs which are found largely on the Pacific coast and in 
the Rocky Mountain region are lowland fir, Abies grandis; white 
fir, Abies concolor; amabilis fir, Abies amabilis; noble fir, Abies 
nobilis, and red fir, Abies magnifica. 

The wood of most of these is light, soft and straight grained; 
it varies in the different species from fine to moderately coarse 



PINES 59 

grained. All of these trees grow to comparatively large size 
and yield excellent pulp wood. With the proper treatment all 
can be satisfactorily reduced by the sulphite process with the 
production of long fibre similar to spruce in quality. White fir 
is already being so treated commercially and yields a long silky 
fibre of the highest quality. All of these firs can be used for 
preparing ground wood for news print work though the color 
of the product is in most cases rather inferior to that of spruce 
ground wood. 

Pines. Longleaf pine, Pinus palustris, ranges from southern 
Virginia to Florida and eastern Texas and northward to north- 
eastern Alabama and northwestern Georgia. Covering a con- 
siderable portion of the same territory is shortleaf pine, Pinus 
echinata. The wood of both is hard, strong, dense, durable and 
resinous and is much used for many grades of lumber. It 
cannot be cooked successfully by the sulphite process because 
of its resinous nature, but if treated by the soda or sulphate 
process it yields a very strong, long-fibred stock suitable for 
wrapping or kraft papers but not for bleaching. 

Jack pine, Pinus divaricata, is found from New Brunswick 
to New Hampshire, westward through the Great Lake region 
to the Rocky Mountains and south into northern Maine, New 
York, Indiana, Illinois and central Michigan. It is not suitable 
for use in the sulphite process but is largely used for the pro- 
duction of kraft pulp by the sulphate process. This wood also 
yields a fair grade of ground wood. 

Other pines which are either used commercially or which 
have been proved by semi-commercial tests to be suitable for 
use in the sulphate or ground wood processes are: white pine, 
Pinus strobus; western yellow pine, Pinus ponder osa; lodgepole 
pine, Pinus murrayana; loblolly pine, Pinus taeda; scrub pine, 
Pinus virginiana and red or Norway pine, Pinus resinosa. 
These pines may be reduced by the soda process but the treat- 
ment required is considerably more severe than that given 
poplar and the fibre is not easily bleached. 



60 FIBROUS RAW MATERIAL 

Hemlock {Tsuga canadenis). Range. — Nova Scotia to Min- 
nesota, Wisconsin, Michigan and southward in the mountains 
of the Atlantic region to northern Alabama and Georgia. 

The wood is light, soft, brittle, not strong, crooked grained, 
liable to wind-shake and splinter and is not durable; its color is 
light brown tinged with red, the sapwood usually somewhat 
darker. 

This wood is used to a considerable extent in the sulphite 
process and yields a fibre very similar to spruce though the 
treatment has to be rather more severe than for spruce. It also 
yields a good grade of kraft fibre. In the ground wood process 
a fair grade of fibre can be produced, though it is considerably 
more difficult to handle than spruce. 

A related species, western hemlock, Tsuga heterophylla, has 
fine-grained, pale yellowish brown, light, soft wood which works 
like white pine. It yields a good grade of sulphite fibre and for 
ground wood is far superior to eastern hemlock. 

Larch or Tamarack, (Larix laricina). Range. — From New- 
foundland and Labrador to northern Pennsylvania, Indiana, 
Illinois, central Minnesota and northwestward to Hudson Bay. 

Wood very heavy, hard, strong, rather coarse grained, dur- 
able in contact with the soil; color light brown, the sapwood 
nearly white. 

Larch is reduced by the sulphite process with some difficulty 
and if mixed with spruce or hemlock is likely to cause chips 
and shives. By the sulphate process it can be made into a 
good grade of kraft fibre; it also yields a good grade of ground 
wood except for color which is a decided grayish green. 

Douglas Spruce (Pseudotsuga taxijolia) . Range. — From the 
Rocky Mountain region and northward to central British 
Columbia. 

The wood varies widely in character and grain which may be 
very coarse, medium or fine. The coarse-grained wood is usu- 
ally reddish brown, while the fine-grained is clear yellowish 
brown. The wood is slightly resinous and resembles pine in 
many of its characteristics. 



WHITE BIRCH 6l 

Douglas spruce has been found well suited for making kraft 
pulp and is already used commercially in the sulphite process, 
though it is not so easy to cook and bleach as spruce. 

Poplar {Populus grandidentata) . Ranges from Nova Scotia 
through New Brunswick, southern Quebec and Ontario to north- 
ern Minnesota; southward to Delaware, southern Indiana and 
Illinois. 

The wood is light, soft, not strong, close grained, compact, 
decays rapidly; color light brown, the sapwood nearly white. 
This is the wood most commonly used in the soda process; it is 
almost never used in sulphite mills though it is readily reduced 
by that process. It yields a ground wood of fair color but of 
rather short fibre. 

The three following species are very similar to poplar in 
character of wood and are of practically identical paper making 
value. 

Aspen {Populus tremuloides) . Range. — Southern Labrador 
to Hudson Bay and northwestward to the Mackenzie River 
and Alaska; southward to Pennsylvania, northeastern Mis- 
souri, southern Nebraska, and throughout the western moun- 
tains to northern New Mexico and Arizona and central California. 

Balm of Gilead {Populus balsamifera) . Range. — Coast of 
Alaska and valley of Mackenzie River to Hudson Bay and 
Newfoundland; southward to northern New England and New 
York, central Michigan and Minnesota, northwestern Nebraska, 
northern Montana, Idaho, Oregon and Nevada. 

Cottonwood {Populus deltoides). Range. — From Quebec and 
Vermont through western New England and New York, Penn- 
sylvania, Maryland, and Atlantic States to western Florida and 
west to the Rocky Mountains. 

White Birch — Gray Birch {Betula populifolia) . Range. — 
From Nova Scotia, New Brunswick, and Lower St. Lawrence 
River southward to Delaware and westward through northern 
New England and New York to Lake Ontario. 

The wood is light, soft, not strong, close grained, not durable; 
color light brown with thick, nearly white sapwood. 



62 FIBROUS RAW MATERIAL 

This wood is easily reduced to pulp by the soda process and 
the fibre bleaches readily. The chief difficulty in its use is in 
the economical removal of the bark. 

Paper Birch (Betula papyrifera) . Range. — From Labrador 
to Hudson Bay, Great Bear Lake, Yukon River and coast of 
Alaska; southward to New York, northern Pennsylvania, cen- 
tral Michigan and Minnesota, northern Nebraska, Dakota, 
northern Montana and northwestern Washington. 

The wood is light, strong, hard, tough and close grained; its 
color is light brown tinged with red and the sapwood is nearly 
white. The bark is removed from this wood with some diffi- 
culty and as even the inner bark causes dirt in the pulp it must 
be very completely removed. 

Paper birch cooks by the soda process with a little more 
difficulty than poplar and the fibre requires slightly more bleach. 
It yields pulp similar to poplar and fully equal to it in quality. 

Red Alder {Alnus oregona). Range. — From Sitka through 
the coast ranges of British Columbia, Washington and Oregon 
to California. 

The wood is light, brittle, fine grained; color pale reddish- 
brown. 

By the soda process this wood cooks readily, yielding a fibre 
very similar to poplar. 

Beech (Fagus atropunicea). Range. — Nova Scotia to Lake 
Huron and Northern Wisconsin; south to western Florida and 
west to southeastern Missouri and Texas. 

The wood is very hard, strong, tough, very close grained, not 
durable in contact with soil, inclined to check on drying; color 
dark or light red with nearly white sapwood. 

Beech cooked by the soda process requires about the same, or 
possibly a little more severe treatment than poplar. The pulp 
is soft and easily bleached, though not quite so easily as 
poplar. 

Chestnut (Castanea dentata) . Range. — From southern Maine 
to nortwestern Vermont, southern Ontario and the southern 
shores of Lake Ontario to southeastern Michigan; southward 



SWEET GUM 63 

to Delaware and southeastern Indiana and on the Allegheny 
Mountains to central Kentucky and Tennessee, central Ala- 
bama and Mississippi. 

The wood is light, soft, not strong, coarse grained, liable to 
check and warp in drying, easily split, very durable in contact 
with soil. It is reddish brown in color. 

Chestnut wood contains tannin which can be profitably ex- 
tracted for use in tanning or other industries. The extracted 
chips can be reduced quite readily by the soda process and the 
fibre bleaches without much difficulty. If the tannin is not 
removed the fibre is hard to bleach. Chestnut fibre is short 
and is used as a substitute for poplar. 

Cucumber Tree (Magnolia acuminata). Range. — From west- 
ern New York through southern Ontario to Illinois and south 
in the Appalachian Mountains to southern Alabama and north- 
eastern Mississippi; central Kentucky and Tennessee. 

The wood is soft, light, not strong, close grained and easily 
worked; color light yellow with nearly white sapwood. 

This wood reduces easily by the soda process giving a fibre 
closely resembling poplar in its paper making value. 

Tulip Tree (Liriodendron tulipifera) . Range. — From Rhode 
Island to southwestern Vermont and west to Lake Michigan; 
south to Florida, southern Alabama and Mississippi. 

The wood is light, soft, brittle, not strong, easily worked; its 
color is light yellow or brown with creamy white sapwood. 

Tuliptree is readily reduced by the soda process, yielding a 
fibre which is similar in character to poplar though generally a 
trifle longer. 

Sweet Gum (Liquidamber styraciflua) . Range. — From Con- 
necticut to southeastern Missouri and Arkansas; south to Florida 
and Texas. 

The wood is heavy, hard, not strong, straight and close 
grained, inclined to shrink and warp badly in seasoning; color 
bright brown tinged with red, sapwood nearly white. 

Sweet gum can be treated by the chemical processes about as 
easily as poplar: the fibre is considerably longer than poplar 



64 FIBROUS RAW MATERIAL 

but not long enough to bring it into the class with spruce and 
other coniferous woods. 

Sycamore {Platanus occidentalis) . Range. — From south- 
eastern New Hampshire and southern Maine to northern Ver- 
mont and Lake Ontario; west to eastern Nebraska and Kansas, 
and south to northern Florida, central Alabama, Mississippi, 
and Texas. 

The wood is rather light, hard, coarse grained, not very strong, 
very hard to split. 

Sycamore cooks easily by the soda process and the fibre is 
longer and more slender than that from poplar; it is said, how- 
ever, to give a rather "punky" paper. 

Sugar Maple, Hard Maple {Acer saccharum). Range. — 
From southern Newfoundland to Lake of the Woods and Min- 
nesota; south to northern Georgia and western Florida; west 
to eastern Nebraska, Kansas and Texas. 

The wood is heavy, hard, strong, tough and close grained; in 
color it is light brown tinged with red. 

By the soda process it is reduced by about the same treat- 
ment given poplar; the fibre is shorter than poplar but bleaches 
readily. 

Silver Maple, White Maple (Acer saccharinum) . Range. — 
From New Brunswick to western Florida; west to southern 
Ontario, through Michigan to eastern Dakota, Nebraska and 
Kansas. 

The wood is moderately light, hard, strong, close grained, 
easily worked but rather brittle. 

It is reduced by the soda process as readily as poplar and 
makes a paper of practically the same quality. The fibre is 
a little shorter than poplar and bleaches readily. 

Red Maple (Acer rubrum). Range. — From New Brunswick, 
Quebec and Ontario to Florida; west to Lake of the Woods, 
eastern Dakota, Nebraska and Texas. 

The wood is very heavy, close grained, not strong; its color 
is light brown slightly tinged with red, the thick sapwood is 
lighter colored. 



BULK OF RAW MATERIALS 65 

Red maple is slightly more difficult to treat than poplar, 
the fibre is rather shorter than poplar and bleaches a little 
harder. 

Basswood (Tilia americana). Range. — From New Bruns- 
wick to Virginia, Georgia and Alabama; west to Lake Superior, 
Lake Winnipeg, eastern Dakota, Nebraska, Kansas and Texas. 

The wood is light, soft, not strong, very close grained, com- 
pact and easily worked; color, light brown tinged with red. 

It is very easily reduced by the soda process and yields an 
easy bleaching pulp very similar to poplar. 

Black Gum ( Nyssa sylvatica) . Range. — From Maine to 
Florida and west to southern Ontario, southern Michigan, south- 
eastern Missouri and Texas. 

The wood is heavy, soft, strong, fine grained, very difficult 
to split; in color it is light yellow or nearly white. 

By the soda process it cooks nearly as easily as poplar and 
yields a fibre free from shives. It bleaches a little harder than 
poplar. Its fibre is longer than that from poplar and makes 
an excellent paper. A very white ground wood can be made 
from it but it has not sufficient strength for newspaper work. 

Bulk of Raw Materials. 

This is an important factor to be considered in the trans- 
portation, storage and cooking of the different materials yet 
very few figures have apparently been published. The follow- 
ing notes therefore make no claim to completeness but are 
merely an attempt to collect in one place what little informa- 
tion is available. 

Rags. Bales of rags as received at the mill have been found 
to have the following weights : 

Lbs. per cu. ft. 

Egyptian rags 37. 5 

Blue cottons 26. 5 

White cottons 19. 5-22. 1 

When dusted and dumped into bins, but not tamped, they 
weigh 15.6 lbs. per cu. ft. before cutting. 



66 FIBROUS RAW MATERIAL 

Straw. Weighings of rice straw gave the following results: 

Lbs. per cu. ft. 

As baled for shipment 1 1 

Chopped and tamped 4.7 

Chopped and not tamped 3.3 

Esparto. Beadle and Stevens 1 give the figures for esparto 
as 120 cu. ft. per ton when pressed as usual or 90 cu. ft. from 
hydraulic presses. 

A boiler of 540 cu. ft. capacity (vomiting type) will hold 50 
cwt. of esparto, which after cooking will occupy a volume of 
300 cu. ft. 

Wood. The number of cubic feet of solid wood per cord 
and the consequent weight per cord vary greatly with the 
different kinds of wood and the size of the logs. Graves 2 gives 
the following table for the number of solid cubic feet for sticks 
of various diameters. 



Diameter of 


No. of sticks 
per cord 


Solid cubic feet per cord of 


sticks 


Hardwoods 


Softwoods 


Mixed 


Ins. 

6.8 

6.0 

4-75 

3-5 


94 
126 
205 
378 


102 .40 
94.72 
88.32 
79-36 


102 .40 
98.56 
97-28 
90.88 


IO2.40 
96.OO 
92.16 
84.48 



Measurements by the author on carefully stacked poplar 
wood in four-foot lengths also illustrate the same point: 



Average diam- 
eter of sticks 


No. of sticks 
per cord 


Weight per cord, 
air dry 


Per cent moisture 


Weight per cord, 
bone dry 


Ins. 

11 .72 

7-9° 

3-i8 


35-5 
70.5 


Lbs. 

4295 
3610 
2625 


34-2 
29-3 
19.7 


Lbs. 

2828 

2553 
2108 







Sound poplar wood when chipped, blown into a bin and 
leveled off but not tamped occupied a space of 259 cu. ft. per 

1 Beadle and Stevens: Chem. News, 1914, 109, 302-304. 

2 Graves: Forest Mensuration, p. 105. 



BULK OF RAW MATERIALS 67 

cord of wood for an average of three tests. The chips, when 
placed loosely into a measuring box, weighed 10.8 lbs. per cu. ft. 
and if thoroughly shaken down but not tamped 13.8 lbs. per 
cu. ft. 
Spruce wood gave, in the case of one test, the following figures: 

One cord air dry spruce with bark weighs 4500 lbs. 

Same after disc barking weighs 3600 lbs. 

Volume of chips from above is 260 cu. ft. 

One cubic foot of chips weighs 13 lbs. 



CHAPTER III 
RAGS, ESPARTO, STRAW, BAMBOO 

Treatment of Rags. It is generally conceded that about 
70 per cent of the rags used in this country are imported, while 
the remaining 30 per cent are collected chiefly in the larger 
American cities where the conditions of sorting are not con- 
ducive to cheapness or good results because of the high rentals 
for buildings and the unskilled labor which must be employed. 
In Europe each family keeps a separate bag for linen, woolen 
and cotton rags. These are collected at frequent intervals and 
are sorted and packed in large sheds which are rented cheaply, 
thus securing less costly and more satisfactory grading. 

The grades of rags differ in different countries and vary 
from time to time. Among those listed in current trade jour- 
nals are the following, which may be taken as generally char- 
acteristic. 

Domestic Foreign 

No. 1 New white shirt cuttings New white cuttings 

No. 2 New white shirt cuttings Unbleached cottons 

Fancy new shirt cuttings Light flannelettes 

New blue cottons New mixed cuttings 

New mixed cottons New dark cuttings 

New black cottons White linens, Nos. 1, 2, 3, 4 

New light second cottons Old extra light prints 

No. 1 Whites Ordinary light prints 
No. 2 Whites • Medium light prints 

House standard whites Dutch blue cottons 

Soiled standard whites German blue cottons 

Thirds and blues German blue linens 

Black stockings Checks and blues 

Dark cottons 

The moisture in baled rags as received at the mill has been 
found from a long series of tests to vary from 7 to 16 per cent 

68 



TREATMENT OF RAGS 



69 




70 RAGS, ESPARTO, STRAW, BAMBOO 

with an average of about 10 per cent. While rags are never 
purchased on the basis of a definite percentage of moisture, as is 
wood pulp, they should be tested at intervals to see that they are 
not intentionally wetted with the object of defrauding the buyer. 

The first process in the mechanical treatment of rags is gener- 
ally a dusting or thrashing. The bales are opened and the 
loosened-up rags thrown into the thrasher, which is usually a 
rapidly revolving cylinder covered with teeth or spikes enclosed 
in an outer cylindrical casing also fitted with teeth. There are 
various types of dusters but the object of all is to free the rags 
from loose dirt and deliver them sufficiently clean for the next 
operation, which is that of sorting into the numerous arbitrary 
grades maintained at the mill in question. This second grad- 
ing is desirable, because they are frequently very imperfectly 
sorted before baling as is shown by tests on seven different 
lots of linens, which, when examined at an American mill, were 
found to contain from 10.5 to 45 per cent, by weight, of cottons. 
During this sorting the larger rags are usually cut into two or 
three pieces, the seams are opened and buckles, buttons, hooks, 
iron, rubber, etc., are removed. Considerable skill and judg- 
ment are required to sort and grade rags correctly and much 
of the success of subsequent operations depends on the care 
with which it is done. The next step in the process is that of 
cutting the sorted rags into pieces 2 to 4 inches square. This 
is generally done by machinery though for the very highest 
grades hand cutting is preferred because it gives cleaner stock. 
Machine cutting causes greater waste in the form of dust and 
many bits of rag are also lost; the rags are also more stringy 
and do not empty from the rotary as quickly as hand cut rags. 
After cutting, the rags are given a final dusting in some form of 
willow which permits the dust to pass through the wire covering 
while the cleaned rags are delivered into cars and are ready to 
be conveyed to the boilers. 

The object of the boiling process is to dissolve or saponify 
the grease, loosen up the dirt and other impurities so that 
they may be easily washed out, and destroy or so modify the 



TREATMENT OF RAGS 7 1 

coloring matters that they may be easily bleached. Another im- 
portant duty is that of destroying any wool which was not 
removed during sorting. The agents used to effect these changes 
are caustic lime, caustic soda or a mixture of lime and soda ash. 
The question of which to use is largely one of personal pref- 
erence and of the type of boiler used. Lime is only slightly 
soluble in water, one part dissolving in 1500 parts of water at 
212 F. or in 728 parts at 68° F. It forms insoluble compounds 
with the grease and other impurities in the rags and is thus 
removed from solution, but as soon as it is precipitated a fresh 
portion dissolves to take its place so that the strength of the 
solution is practically constant throughout the boiling. This 
slight solubility of the lime limits the speed of reaction and the 
only way to make up for it is to increase the time of treatment. 
On the other hand, it prevents injury to the fibres from too 
great concentration of alkali and is therefore more likely to 
give good results when the usual, unscientific, hit-or-miss methods 
of control are employed. 

Caustic soda acts in the same way as lime except that it is 
readily soluble in water and the compounds formed also remain 
in solution and are therefore more easily washed out. Because 
of the complete solubility of caustic soda its use subjects the 
rags at first to strong solutions which continually diminish in 
strength as the treatment continues. If the caustic soda used 
is the chemical equivalent of the lime generally employed the 
rags will probably be overcooked and tender and the yield 
low, but if the caustic soda is used in smaller amounts and the 
time of boiling properly regulated there is no reason to think 
that it will give inferior fibre or a lower yield than a lime cook 
on the same stock. Lime-boiled rags are brighter in color than 
those boiled with soda but this difference frequently disappears 
after bleaching. The rapidity with which the alkali is "used 
up in a soda boil is shown by the following condensed data 
from large scale experiments by Beadle. 1 

1 Chem. News, 1901, 84, 257. 



72 



RAGS, ESPARTO, STRAW, BAMBOO 



Rags 


Gals. 

per 
cwt. 


Liquor, 

per cent 

Na 2 


Per cent 

Na 2 on 

rags 


Free Na 2 at hours below, start 
being 100 per cent 


1 


2 


3 


4 


S 


i and 2 cottons . . . 


24 

25-7 
22—22.5 

23-25 


°-33 

O.654 

O . 55-O . 90 

O.91-I .36 


0.697 

1.68 
1 .22-1 .78 
I-9I-2-45 


38 

48 

31-70 

25-80 


15 

24 

21-43 

16-24 


8 

19 

13-26 

9-19 






2nd cottons 






3rd cottons 

Linens 


IO-23 

7-13 


•-I3 



The severity of the treatment given rags varies greatly in 
different mills and with the grade of rags and the kind of paper 
to be produced. The caustic soda necessary is given by dif- 
ferent authorities as from i to 10 per cent, while the use of lime 
varies from 5 to 20 per cent on the weight of the rags. The 
steam pressure runs from 15 to 50 lbs., with 30 lbs. as probably 
a fair average, while the time of boiling ranges from 2 to 14 
hours, and in some cases has been as much as 30 hours. Lime 
necessitates longer cooks than soda but the tendency in all 
cases is toward the shorter cooks since the steam consumption 
is less and the yields and the capacity of the plant are greater. 
Watt 1 gives the European practice as 12 hours at 30 lbs. steam 
pressure using 216 to 378 lbs. of lime and 114 to 190 lbs. of 48 
per cent soda ash for 4000 lbs. of rags. In general it may be 
said that dark-colored or very dirty rags require much more 
severe treatment than new cuttings or clean, light-colored stock. 

The presence of starch in new cuttings is said to interfere 
with the boiling by gelatinizing and preventing the penetration 
of the alkali. It has been proposed to get around this diffi- 
culty by the use of malt to hydrolyze and remove the starch. 
The rags are boiled with water to swell the starch, cooled to 
6o° C. by adding cold water, and an infusion of malt is then 
added. In one to two hours hydrolysis is sufficiently complete 
so that alkali may be added and the boiling completed in the 
usual way. 

The .lime used should slake rapidly and completely and should 
be as free as possible from iron. It is generally conceded that 

1 Watt: Art of Paper Making. 



TREATMENT OF RAGS 73 

its value for this work is in proportion to its content of avail- 
able calcium oxide. In preparing it for use it should be slaked 
and run into the boiler through wire sieves to take out any 
lumps. Griffin and Little 1 give the following analysis of lime 
as representing an excellent grade for rag boiling. 

Per cent 

Silica, etc., insoluble in acid o. 01 

Iron and alumina (Fe 2 03 and AI2O3) o. 28 

Lime (CaO) 92-81 

Magnesia (MgO) 2. 28 

Moisture, Carbonic Acid, etc. (by difference) 4.62 

100. 00 

The volume of milk of lime added to a rotary boiler is gener- 
ally enough to fill it from one-half to two-thirds full after the 
rags are in. If the rags are not covered by the milk of lime, 
but are exposed to the steam, they may become tender and 
brittle. 

Several types of boilers are used for cooking rags; spherical 
or cylindrical rotary boilers and stationary boilers in which the 
circulation of the liquor is maintained either by a pump as in 
the Mather kier or by a vomiting pipe which is connected 
with a false bottom. In this case the steam enters under the 
false bottom and in passing up the pipe carries along the cooking 
liquor which is then distributed over the charge by baffle plates. 
The stationary type of boiler is fitted with a safety valve and 
there is therefore less danger of explosion than with the rotaries. 
It is claimed that there is less loss of fibre because the rags are 
not in motion and hence there is no rubbing off of the weaker 
fibres. On the other hand, they require more steam, are not 
suitable for use with lime cooks and take longer to discharge, 
since the cooked rags must all be removed by hand through 
manholes. Stationary boilers are largely used in Great Britain 
but seldom on the Continent or in this country. 

Of the rotary boilers the cylindrical is more generally em- 
ployed than the spherical, though the shape of the latter greatly 
assists in discharging its contents. The boilers are charged 

1 Griffin and Little: Chemistry of Paper Making, p. 152. 



74 



RAGS, ESPARTO, STRAW, BAMBOO 



through manholes and with large boilers the men frequently 
enter them in order to pack the rags properly. The steam 
enters the boiler through the trunions and passes through grat- 
ings on the inside into the stock. The rotaries are also fitted 
with strainers through which much dirt passes in blowing off 
pressure. The rotaries usually turn at a speed of one revolu- 




Fig. 5. Spherical Rag Boiler 

tion in two to five minutes. The consequent agitation and 
friction of the rags cause the detachment of the lime compounds 
formed and allow the action to continue on the remaining fatty 
materials. When the cook is completed the liquor and steam 
are blown off through the strainers and blow-off cocks, the 
manhole covers are removed and the contents are discharged 
by allowing the boiler to revolve. Even a large cylindrical 
boiler will empty itself clean in this way. With competent 
labor the operations on a cylindrical boiler holding a charge of 
5000 to 5200 lbs. of rags occupy the following times: 

Hours 

Charging rags if 

Blowing off liquor 2 

Discharging rags 3 

During the cooking of rags a small amount of ammonia is 
given off. Tests on a large scale showed that the following 
amounts were discharged. 



TREATMENT OF RAGS 75 

o. 22 per cent ammonia (NH 3 ) from Japanese blues, 
o. 05 per cent ammonia (NH3) from second white stock 
o. 14 per cent ammonia (NH 3 ) from clean white linen 
o. S3 P er cent ammonia (NH 3 ) from German blues 

The washing of the cooked rags is usually done in large en- 
gines similar to beating engines. One or more cylinder washers 
covered with perforated metal or wire cloth, frequently old 
Fourdrinier wire, serve to remove the dirty water which is 
constantly replaced by fresh water. If the rags are allowed to 
stand some time with the lime on them before washing they 
become softer and more absorbent and are better for blotting 
papers. On the other hand, if they are washed at once they 
are harder and the color is rather better. The lime compounds 
formed during cooking are friable and easily washed out in 
most cases but occasionally enough mineral oil is present so 
that they collect in sticky masses on the sides of the washer, 
fill up the meshes of the wire on the washing drum, and appear 
as small globules in the rag stock itself. When lime is used the 
washing should always be done with cold water because of the 
greater solubility of lime at low temperatures. 

When the water from the cylinder washer comes away fairly 
clear the beater roll is lowered to loosen up the remaining dirt 
and gradually reduce the rags to half stuff. If this is done too 
soon the fibre loss is unduly great and the frayed out fibres 
catch and hold the dirt and the resulting stock is of poor color. 
After the rags are reduced to half stuff the bleach is added to 
the engine and the whole put into drainers to complete the 
bleaching. 

The amount of water used in preparing rag stock is very con- 
siderable. Sindall 1 states that the water required to wash the 
rag stock for a ton of paper is 25,000 to 35,000 gals. Beadle 2 
estimates the quantity used in preparing the rags for one ton of 
two grades of paper to be as follows, measurements being in 
Imperial gallons. 

1 Sindall: Paper Technology. 

2 Beadle : Chapters on Paper Making, Vol. IV. 



7 6 



RAGS, ESPARTO, STRAW, BAMBOO 





Bank paper 


Rag paper 


Boiling rags 


1,500 
1,500 

40,000 
5.000 

48,000 




Rinsing rags 




Washing in engines 


37.830 
5,000 

43.930 


Washing out bleach 





The losses which rags undergo in making into paper vary 
enormously with the quality of the rags and the treatment they 
are given. The following table, condensed from data in Hof- 
mann's "Papier Fabrikation" shows the losses in preparing 
half stuff from different materials. 



Kind 



White linens 

Bagging 

White cotton 

Red and blue calico. . . 
Half wool and old rags 
Blue linen 



Mois- 
ture 



Per cent 

5-7 
5-i 1 
4-5 

6 

6 
6-7 



Cutting 

and 
dusting 



Per cent 
4-5 
5-7 

5 

6 

6 

6 



Cook- 
ing and 
wash- 
ing 



Per cent 

7-12 

II-18 

n-13 

12-13 

38 
IO-13 



Beat- 
ing to 
half 
stuff 



Per cent 

4-9 
12-14 

8-9 
12-13 

10 

9-14 



Bleach- 
ing 



Per cent 
3-6 
5-9 

4 
4-5 

4 
4-5 



Total 
loss 



Per cent 
26-33 
42-55 

34 
40-42 

64 

35-45 



Kilos 

bone dry 

half stuff 

per 100 kg. 

rags 



67-74 

58-45 

66 
58-60 

36 
55-65 



Similar data from the records of an American book paper 
mill using rotary boilers are: 



Kind 



Sorting 
and tare 



Thrashing 



Cutting 



Total loss 

to finished 

paper 



Japanese blues 

New calico 

Belgian blues 

Whites 

Muslins 

Russian blue linens 



Per cent 
3. 



Per cent 
2.4 
4.0 

4-9 
0.2 

1.8 
2-5 



Per cent 
3-6 
0.4 
2.8 
5-o 
3-i 
6-7 



Per cent 
34-6 
26.2 
42 .2 
25-5 
4i-7 
45-8 



Beadle x in recording English practice gives the following 
figures for the losses on boiling and bleaching. 

1 Beveridge: Paper Makers' Pocket Book. 



ESPARTO 



77 



Best new cottons 

Low grade cottons 

No. i cotton rags 

No. 3 cotton rags 

New unbleached cottons 



Percentage lost on 



Boiling 



Per cent 

8.71 

12.20 

5-8o 

12.50 

2 3S° 



Bleaching 



Per cent 
.29 
.70 
.20 



Esparto. Esparto, because of its high cost, has never come 
into competition in this country with soda fibre prepared from 
woods, but in Europe, and more particularly in Great Britain, 
it is one of the most important fibrous raw materials. Intro- 
duced into England in i860 by Routledge, its use increased 
from 16 tons in 1861 to 184,000 tons in 1884, since which time 
about 200,000 tons have been used every year, not including 
what is used on the Continent. 

The grass is imported in bales bound with iron or twisted 
bands of esparto. These bales are opened up and spread out 
on tables covered with iron netting to allow sand and dirt to 
pass through, and the grass is sorted by hand to remove roots, 
weeds, etc., which are more resistant to alkali than esparto and 
hence cause dirt and shives in the pulp. The loss in dusting 
and hand picking is 1 to 6 per cent. The dust contains sand 
and other mineral matter as well as fat or wax from the esparto 
itself. The analysis of fine dust is given by Beveridge * as 
follows : 

Per cent 

Organic matter (by ignition) 64. 6 

Water (loss at 212 F.) 6_ 2 

Mineral matter 2 n 2 

Of the organic matter, about 90 per cent is of a waxy nature, 
while the mineral matter or ash gave the following analysis: 

1 Beveridge: Paper Makers' Pocket Book. 



78 RAGS, ESPARTO, STRAW, BAMBOO 

Per cent 

Silica (Si02) 56. 43 

Calcium carbonate (CaCOs) 19. 17 

Magnesium carbonate (MgCOs) 3-76 

Alumina (AI2O3) 20. 57 . 

99-93 

Machine cleaning by willows is also resorted to and by some 
is considered superior to hand picking. The grass from the 
willows goes directly to the cookers without any further sorting, 
and sand and uncooked weeds, etc., are removed by sand traps 
and screens after cooking. 

The boilers used for esparto may be merely open tubs since 
little or no pressure is necessary but the more general practice 
is to employ closed, stationary boilers with some device for cir- 
culating the liquor. Rotary boilers are almost never used as 
they cause the fibres to roll up into small balls which beat out 
with great difficulty and are apt to cause lumps in the paper. 
The capacity of esparto boilers is generally 2 to 3 tons of grass. 
The boiler is partly charged with lye and the esparto is fed in, 
steam being admitted at the same time to soften it and enable 
a greater quantity to be packed in. The grass, which is not 
cut as in the case of straw, is charged through the top and after 
cooking is removed through a side door near the bottom. The 
steam pressure carried varies in different mills from 5 to 50 lbs., 
and the time of cooking from 2 to 6 hours; the present tendency 
seems to be toward the higher steam pressures. 

As compared with rags esparto requires a much greater 
amount of alkali, which is invariably soda, since lime is never 
used because of the formation of insoluble compounds. The 
amount of alkali recommended by Dunbar for different grades 
of grass is as follows: 

Fine Spanish 16. 1-17. 9 lbs. 70 per cent caustic per 100 lbs. grass 

Medium Spanish.. 14. 3-16. 1 lbs. 70 per cent caustic per 100 lbs. grass 

Fine Oran 16. 1 lbs. 70 per cent caustic per 100 lbs. grass 

Medium Oran. ... 14. 3-15. 2 lbs. 70 per cent caustic per 100 lbs. grass 

Tripoli 17. 0-17. 9 lbs. 70 per cent caustic per 100 lbs. grass 



ESPARTO 



79 



The liquor for boiling varies from 7 to 15 degs. Tw. 
As typical examples of actual cooks made under fairly good 
working conditions Beveridge 1 gives the following: 



Weight of charge 

Caustic liquor per charge, gals. . . 
Pounds of 60% caustic per charge 

Steam pressure, maximum 

Time under pressure 

Yield, unbleached air dry fibre . . 



Spanish 



5600 lbs. 
I570 
900 
20 lbs. 
2§ hrs. 
44-45% 



Tripoli 



5600 lbs. 
I570 
1020 
20 lbs. 
3 hrs. 
41-42% 



When the cook is completed the pressure is blown down and 
the liquor run off to the recovery system; hot water is then run 
into the boiler and the pressure brought up to 20 to 30 lbs. 
This is again blown off, the stock drained as dry as possible, re- 
moved, and conveyed to the washing system which usually 
consists of engines similar to those used in treating rags. Dur- 
ing washing much of the cellular matter (leaf hairs) is removed 
and some short fibres are lost. 

The bleaching of esparto is generally carried out in engines. 
The bleach required varies from 7 to 12 per cent of the un- 
bleached fibre and often a little sulphuric acid is added to the 
engine about half an hour after the bleach. When bleaching 
is completed the stock is run off on a press-pate which serves 
the double purpose of removing the bleach residues and de- 
livering the fibre in a convenient condition for further operations. 

The recovery of alkali from the waste liquors is conducted 
along the same lines as with the liquors from wood. Accord- 
ing to Griffin and Little 2 the silica in the ash from esparto 
forms silicate of soda during furnacing and thus reduces the 
per cent of ash recovered. A recovery of 80 per cent is con- 
sidered good while 85 per cent is the most that can be expected 
under the best conditions. 

1 Beveridge: Paper Makers' Pocket Book, p. 76. 

2 Griffin and Little: Chemistry of Paper Making, p. 158. 



8o 



RAGS, ESPARTO, STRAW, BAMBOO 



Straw. Straw as used in paper making includes the stems 
and leaves of the various cereals. The composition of straws, 
particularly with regard to the amount of ash and its constitu- 
ents, varies greatly with the soil upon which they were grown. 
Wolff 1 gives the following analyses for different straws. 



Water 

Ash 

Fat and wax 

Nitrogenous matter 

Starch, sugar, gums, etc 
Cellulose 



Winter 
rye 



Per cent 

14-3 

3 
3 
5 

25-7 

54 



Winter 
wheat 



Per cent 
14.2 

5-5 

i-5 

2 .0 

28.7 

48.0 



Sum- 
mer 
barley 



Per cent 
14-3 



Winter 
barley 



Per cent 

14-3 
5 
4 



28 



Oats 



Per cent 

14-3 
5-0 
2.0 

2-5 

36.2 
40.0 



Corn 



Per cent 

14.0 

4.0 

1 .1 

3° 

37-9 

40.0 



Beveridge 2 considers the cellulose as determined by Muller's 
method too high and gives the following percentages obtained 
by digesting the straw with bisulphite of soda. 

Per cent 

French wheat 41.5 

Zealand wheat 40. 9 

Dutch wheat 41. 6 

Dutch oats . . 42. o 

Dutch rye 44. 7 

Dutch barley 38. 3 

Cross and Bevan 3 give the percentage of bone dry cellulose 
on bone dry straw as follows: 

Per cent 

Oats 52.0 and 53. 5 

Oats, foreign 46. 5 

Wheat 49. 6 

Wheat, foreign So. 2 

Rye, foreign 53. o 

From analyses of rice straw by Takeuchi 4 the following figures 
are taken: 

1 Wolff: Landwirtschaftl. Kalender, 1869, zitiert bei Hugo Miiller, Die Pflan- 
zenfaser, p. 97. 

2 Beveridge: J. Soc. Chem. Ind., 1894, 101. 

3 Cross and Bevan: Text Book of Paper Making, 1907, p. 136. 

4 Takeuchi: Bull. Coll. Agric, Tokio, 1908, 7, 619-621. 



STRAW 



Hygroscopic moisture .... 

Dry matter 

Total nitrogen ■ 

Crude protein 

Crude fat 

Crude fibre 

Crude ash 

Silica 

Dextrose 

Sucrose 

Starch and hemicelluloses 
Pentosans 



Good harvest 


Poor harvest 


Per cent 


Per cent 


12.31 


9-85 


87.69 


90 


15 


0.97 


1 


48 


6.05 


8 


82 


I.36 


1 


65 


31.16 


28 


72 


11 .42 


12 


35 


5-39 


6 


13 


2.25 


3 


28 


0.79 





96 


14.86 


18 


75 


14.28 


16 


55 



Analyses by the author of two samples of American grown 
rice straw of the "Carolina Gold" variety showed the presence 
of 14.5 and 12.4 per cent of ash of which silica constituted 
81.6 and 79.7 per cent respectively. 

The ash from various straws shows the following compo- 
sition: 1 





Total 
mineral 


K2O 


Na 2 


CaO 


MgO 


Fe 2 3 


P2O5 


so 3 


Si0 2 


CI 


Barley, aver, of 4 
Oat, aver, of 8. . . . 
Rye, aver, of 3. . . . 
Wheat, one test. . . 


% 
8.IO 

7-77 
4-32 
3-25 


% 
23-75 
38.37 
26.28 
12.16 


% 
1 .92 

3-99 
0.74 
1 .00 


% 

7-53 

4-23 

11 .10 

6.82 


% 
2.62 

2-53 
4-45 
4.00 


% 

2.19 
1.79 

3-i9 
1 .02 


% 

3-94 
2.66 

8-97 
3.20 


% 
3-91 
3.06 

5-57 
5-78 


% 
51-43 
35-68 
36.86 
65-34 


% 
3-75 
7-99 
3-68 
0.60 



Straw is used for the production of two quite dissimilar fibrous 
materials; a coarse, yellowish, half stuff which is used for straw 
boards and cheap wrapping papers, and a bleached cellulose, 
similar to esparto in many of its properties, which enters into 
the composition of numerous high grade products. 

For the manufacture of straw boards, the straw, after dusting 
and cutting into short lengths, is treated with milk of lime in 
rotary boilers. The action of the lime is not vigorous, incrust- 
ing matters are not separated from the cellulose to any great 
extent and mineral matters originally present in the straw re- 
main practically untouched in the finished product. According 

1 Wolff: Ashen analysen. 



82 RAGS, ESPARTO, STRAW, BAMBOO 

to Kirchner x it is the general practice in Germany to cook the 
chopped straw in rotary spherical boilers of 14 cubic metres 
(494 cu. ft.) capacity which hold 1100 kilos (2420 lbs.) or 1500 
kilos (3300 lbs.) after tamping. The steam pressure varies 
from 45 to 75 lbs. and the time of cooking from 4 to 5 hours. 
A yield of 70 to 80 per cent is obtained. 

In some plants the lime is slaked and strained into the boiler 
while in others the quicklime is added without slaking. If the 
lime is poor a little soda ash is sometimes added. Rye and wheat 
straw should not be boiled together since wheat needs more 
treatment than rye. For rye straw 8.5 per cent of quicklime is 
sufficient while for wheat 10 per cent is required. It is gener- 
ally reckoned that there is a loss of 30 to 35 per cent of fibre 
substance from the dry straw to the finished paper. 

According to B. Haas 2 the chopped straw and liquor are fed 
into the digester together and gently steamed at the same time, 
thus increasing the capacity of the digester fully 10 per cent. 
The digester should be rotated without steam to distribute the 
liquor, then steamed with the blow-off cock open to allow air 
to escape and finally steamed at 60 lbs. pressure for 2\ to 3 
hours. If handled in this way it is claimed to be possible to 
cook wheat straw with 6 per cent of lime while under ordinary 
conditions it would require 13 to 15 per cent. If too much 
lime is used the resulting stock is " greasy," drains slowly and 
clogs wires and felts. 

In France considerable straw is said to be treated by a cold 
process as follows: Rye straw is cut short and put into large 
rectangular br^ck wells where it is just covered with dilute 
milk of lime. Boards are put on, weighted down with stones 
and the whole left for two to four weeks. It is then taken out 
and worked in edge runners for at least an hour. This product 
is harder than straw pulp cooked by steaming at high tempera- 
tures and as the knots are not softened the grinding must be 
done with especial care. Straw pulp prepared in this way 

1 Kirchner: Das Papier, III, B and C. 

2 Der Papier-Fabr., 12 (1914), 305-310. 



STRAW 8$ 

possesses a natural self-sizing property which is lost if the milk 
of lime is heated and is absent in pulp cooked by the soda pro- 
cess. Hot cooked stuff requires much rosin size because of 
the presence of lime residues which it is impracticable to com- 
pletely wash out. 

The general American practice differs somewhat from the 
German in that the straw is not cut and sorted before cooking. 
The kind most generally used is winter wheat though some use 
rye and oat straw. It is always received at the mill in bales 
which are stored in large stacks near by; these stacks are fre- 
quently provided with roofs and sometimes with shelter on the 
sides. There appears to be little deterioration of the straw, 
except on the very outside of the bales or in those at the bottom 
of the pile, and even such straw, which has become very dark 
in color, is used by adding a little more lime to bring it to the 
right color. In filling the rotaries the bales are broken up and 
immediately fed in without sieving, cutting or any other method 
of preparation; in fact as much as a quarter of a bale is some- 
times added without loosening up in any manner. This is 
done because it is believed a larger charge can be secured. As 
the rotary is filled about a gallon of water is added for every 
2\ lbs. of straw. The rotary is then revolved and steam ad- 
mitted to raise the charge to '25 lbs. pressure which is main- 
tained for half an hour or so. The head is removed, more 
straw added and the charge again steamed or " wilted" as 
before. This is repeated three or four times so that the final 
charge is about double that which was first added. At this 
point milk of lime is added, equivalent to 10 per cent calcium 
oxide (CaO) on the weight of the straw, after which it is rotated 
and brought up to 35 to 45 lbs. steam pressure where it is held 
for 8 to 10 hours. The liquor is drained off under pressure, 
the charge cooled till practically at atmospheric pressure, and 
then dumped onto the floor where it is allowed to season three 
to five days before being used. The straw is washed about 
four hours in washing engines, the washer taken up and the 
beating proceeded with. 



84 RAGS, ESPARTO, STRAW, BAMBOO 

The time required for one cook, including charging, cooking 
and cooling, is about 24 hours. The yield per ton of straw is 
generally figured as 1600 lbs. of board for rye, 1400 lbs. for 
wheat and 1200 lbs. for oat or rice straw. 

The treatment of straw by the soda process for the production 
of a high grade bleached cellulose occupies an important place 
in the paper industry of Europe though it is practically never 
undertaken in this country. The kinds generally used are 
wheat, oat, rye and barley straws, and of these the first two 
are used most extensively in England. Since straw is more 
highly lignified than esparto it requires a more drastic treat- 
ment; even the knots must be so reduced that they will bleach 
readily. Because of this more severe treatment and because 
of the presence of cellular tissues which are lost during the 
washing process the yield from straw is less than that from 
esparto. Cross and Bevan 1 give the practical yield as about 
35 per cent, while Beveridge 2 says that a mixture of equal 
quantities of barley, oat, wheat and rye straws will yield 40 to 
41 per cent of air dry bleached cellulose. 

The straw cellulose makes a weaker paper than esparto but 
it is suitable for mixing with rags or wood pulp for thin, hard, 
rattly papers. It tends to make the stock a wet" on the wire 
and imparts translucency to the papers in which it is used. 

In modern plants the straw is cut by rotary cutters into 
pieces one to two inches long and freed from dust, grain, etc., 
by an air blast. It is then fed into the boilers, steam and alkali 
added at the same time assisting in packing the charge. Contrary 
to the practice with esparto rotary boilers are preferred for 
straw because the agitation of the charge permits a penetration 
of the liquor which cannot be obtained in a stationary cooker 
because of the close packing of the wet straw. The amount of 
alkali used varies greatly at the different mills and with the 
kind of straw; it may run as low as 10 per cent or as high as 
20 per cent of the weight of the straw. Experiments conducted 

1 Cross and Bevan: Textbook of Paper Making. 

2 Beveridge: Paper Makers' Pocket Book. 



STRAW 85 

by the author on rice straw proved that a simple extraction 
with water at 20 to 25 lbs. steam pressure removed so much 
material from the straw that well reduced and easily bleached 
fibre could be produced with 60 to 75 per cent of the caustic 
soda necessary for unextracted straw. Barley straw is said to 
require 20 per cent less soda than oat, wheat or rye straw. The 
time of cooking is variously given as 3 1 to 8 hours and the steam 
pressure as 10 to 90 lbs.; there seems to be a decided tendency 
toward the use of the higher pressures of from 75 to 90 lbs. 

The cooked straw is run or blown from the boiler into wash 
tanks with false bottoms; these are preferred to drum washers 
because of the large loss of fine fibres and cellular matter which 
the latter cause. After washing, the straw is treated in edge- 
runners to crush the knots and it is then bleached in much the 
same way as esparto; the bleach required is from 7 to 10 per cent. 
The recovery of alkali is carried out in the same way as with 
esparto or wood but the working of the process is rendered 
difficult in many instances by the silica in the straw. This 
combines with the alkali forming sodium silicate and when the 
recovered ash is causticized a bulky, gelatinous precipitate of 
calcium silicate results. This prevents settling in the causti- 
cizing tanks and very greatly reduces the amount of soda which 
can be recovered. A patented process by Sutherland and 
Kynaston proposes to precipitate the silica by adding bicarbo- 
nate to the solution of the recovered ash; carbon dioxide can 
also be used. They claim to obtain in this way a granular 
precipitate which can be easily handled, but the process has not 
been an entire success. 

Beveridge r states that the soda lost varies with the amount 
of silica in the straw, with the composition of the silicate formed 
and with the amount of potash rendered soluble. He estimates 
that as much as 42 per cent of the total soda in the cooking 
liquor may be neutralized by the silica and claims that when 
the amount of silica in the straw approaches 3 to 4 per cent 
of its weight the recovered ash is of little value for further 
1 Beveridge: Paper Makers' Pocket Book. 



86 RAGS, ESPARTO, STRAW, BAMBOO 

digestions. The recovery in a Russian mill operating by the 
sulphate process is claimed to be 80 per cent. 1 

Numerous other processes have been suggested for treating 
straw. Chlorination in stone chambers, of straw which has 
been partially cooked with caustic soda, followed by a treat- 
ment with bleach, gives a high yield of well-bleached, uniform 
stock, but the process is too costly and difficult to manage. 
Diess and Fournier 2 propose steeping the straw in acidulated 
water for three hours, retting by organisms cultivated from 
African esparto, and finally cooking with strong caustic soda 
solutions — 20 to 30 Be. — at 45 to 75 lbs. steam pressure 
for three to five hours. Reichman 3 treats the straw with caus- 
tic soda, washes, treats with hydrofluoric acid of i° to 2 Be. 
for about five hours and finally washes with dilute ammonia. 
Probably the only modification of the original soda process which 
has found any extensive use is the sulphate process and this 
has been applied to straw with notable success. 

The sulphite process is not generally applied to straw, though 
in isolated cases good fibre has been prepared from it in this 
way and practical experience has. shown that it can be employed 
with excellent results. The general assumption that the large 
proportion of silica in the straw would interfere with its treat- 
ment by the sulphite process is apparently not founded on fact. 

Bamboo. Bamboo, while not of immediate interest in this 
country, seems destined to hold an increasingly important place 
as a source of fibre because of the rapidity of its growth and the 
high quality of the paper which can be made from it. Raitt 4 esti- 
mates that with poor growth the annual yield of stems would 
be n tons, air dry, per acre while with luxuriant growth it may 
amount to as much as 44 tons. He states that in Lower Burma 
alone there is an area of about 20,000 square miles easily 
available. 

1 Altaian: Chem. Ztg., 191 1, 35, 979. 

2 French Pat. 403, 518. 

3 English Pat. 12,059, May 21, 1909. 

4 J. Soc. Chem. Ind., 1908, 27, p. 35. 



BAMBOO 



87 



Characteristic analyses of Philippine bamboos are given by 
Richmond as follows: : 





Structural 
bamboo 


Dwarf bamboo 


Cellulose 


Per cent 

53-94 

0.96 

4.98 

24-25 

12 .40 

3-47 


Per cent 

55-75 

1.03 

4.69 

21 .27 

11 .20 

6.03 


Fat and wax 


Water extract 


Non-cellulose or lignin 


Water 


Ash 





Analyses of typical absolutely dry Indian bamboos are: 



Cellulose 

Fat and wax 

Water extract 

Pectose 

Lignin 

Ash. 



B. polymorpha 



Per cent 

54.71 

1 -05 

8-95 

19-55 

15-74 

100 . 00 

3-97 



B.arundinacea 



Per cent 

50.32 

1. 17 

8.48 

24-39 

15-64 

IOO.OO 

1 .60 



C. pergracile 



Per cent 

52.73 
0.92 
7.96 



By an extended research on the five most likely Indian bam- 
boos, Raitt 3 has shown that by the soda process yields of 41.0 
to 43.0 per cent of bleached fibre may be obtained, but the 
bleach consumption is high. When the sulphate process is 
used the yields are 42 to 44 per cent and the bleach required 
is much lower— 15.5 to 18.0 per cent. He finds the sulphite 
process is unsuited to bamboo because of the- difficulty of bleach- 
ing the fibre and of working with sulphite liquor in a tropical 
climate. 

Raitt overcame the difficulties previously encountered with 
bamboo by adopting the following treatment: 

(1) Culms not to be cut till the shoots of the year are full 
grown. 

1 Richmond: Philippine J. Sci., I, 1906, 1075-1084. 

2 Raitt: Indian Forest Records, Vol. Ill, Part III, p. 15. 

3 Raitt: Indian Forest Records, Vol. Ill, Part III. 



88 RAGS, ESPARTO, STRAW, BAMBOO 

(2) Seasoning for at least three months before use. 

(3) Crushing. 

(4) Extraction of starchy matter. 

(5) Digestion with sulphate liquor. 

The limiting conditions of satisfactory digestion for the five 
species investigated were found to be 20 to 22 per cent caustic 
soda (including the sodium sulphide), temperatures of 162 to 
177 degs., pressures of 80 to 120 lbs., and durations of 5 to 6 
hours. 

Old Papers. In the case of old printed papers of the higher 
grades, such as book and magazine papers, in which there is no 
ground wood, little difficulty is experienced in preparing them 
for use a second time. The removal of the printer's ink can be 
effected by ■ cooking in digesters with a caustic soda solution 
followed by disintegration and washing of the pulp. The alkali 
removes the rosin sizing and saponifies the oily constituents of 
the ink thus rendering them soluble and loosening the pigments 
so that they may be detached from the surface of the fibres 
and washed out. 

In this process, as applied to old magazines for instance, the 
staples are removed by mechanical means and the magazines 
fed into rotary digesters. The removal of the staples allows 
them to come to pieces sufficiently so that the alkali can pene- 
trate enough to reach all parts of the paper and opening up 
by thrashers is therefore not necessary. About 3 to 4 per cent 
of caustic soda, on the weight of the papers, is then added 
together with enough water to insure thorough saturation of 
the charge and it is cooked at 40 to 50 lbs. steam pressure for 
a number of hours, sometimes as long as 13 hours. After blow- 
ing down pressure the rotary is dumped and the stock allowed 
to drain, after which it is transferred to washers and washed 
and bleached in practically the same manner as rag stock. 
The time required for washing varies greatly with the size and 
condition of the washing engine, it may even go as high as 15 
hours although this is not usual if the stock has been well 
drained. The bleach required amounts to 3 to 4 per cent of the 



OLD PAPERS 89 

papers used and the color obtained is usually a grayish white 
because of the impossibility of removing all traces of the carbon 
from the printer's ink. This process involves a considerable 
loss due first to the action of the soda and steam in the digester 
and second to the mechanical loss of fine fibres and the mineral 
fillers during the washing. The combined loss from these 
causes will frequently amount to 35 to 40 per cent of the 
absolutely dry papers used. 

Similar results are obtained by tearing the papers up some- 
what and heating in large boilers with an 8 to 10 per cent solu- 
tion of soda ash. The temperature is maintained just below 
the boiling point as the object is merely a surface loosening of 
the ink and not complete disintegration of the paper to a fibrous 
stock. 

It has also proved possible to eliminate the rotary digester and 
carry out the entire process in the beating engine or washer. 
The printed papers, either plain or coated, are fed into the 
engine with water and about 2 per cent of caustic soda based on 
the papers. When warmed to 120 F. they disintegrate readily 
and in a short time the washing can be started and carried out 
as usual. The color of the stock obtained is better than that 
of the material cooked in rotaries and the loss is probably 
slightly less. The chief objection to the process is that the old 
magazines which are largely used have to be thoroughly broken 
up before adding to the beater. 

In either of these processes ground wood has to be carefully 
avoided because it is turned brown by the alkali, yet is not 
cooked enough so that it will bleach to a good color. Serious 
trouble has been caused at times by getting ground wood papers 
into the rotary and it is well to supply the sorters with phloro- 
glucin or paranitro-aniline so that they may test suspected 
papers and throw aside all those found to contain ground wood. 
Stock which contains ground wood, after passing through the 
rotaries and bleachers, has the appearance of being contami- 
nated with fine, brown hairs or fibres. These are very con- 
spicuous when such print papers are used in a white sheet. It 



90 RAGS, ESPARTO, STRAW, BAMBOO 

is interesting to note that after cooking the ground, wood is 
just enough changed so that it gives no test, or at most a very- 
faint pink, with phloroglucin. 

This explains why it has proved so difficult to recover the 
stock from old newspapers, which consist of approximately 
three-quarters ground wood. The problem has, however, proved 
very attractive to a large number of investigators and the 
patents taken out are very numerous. Among the reagents 
which it has been proposed to use are various alkalis and alka- 
line salts, silicates, borates, phosphates, etc., soaps, peroxides, 
hypochlorites, aluminum chloride, enzymes and inert materials, 
such as clay, talc, fuller's earth, etc. These latter seem to be 
added to serve as points about which the pigments from the. 
ink may gather and thus facilitate their removal by the washers. 
Most inventors are not content with adding single reagents or 
even simple combinations of two or three, but in cases use as 
many as eight different substances at the same time. Any 
such combinations to be of value in treating ground wood 
papers must be only weakly alkaline and must be used at com- 
paratively low temperatures. Among the materials which have 
been found best for this purpose are fatty soaps and similar 
materials used in conjunction with soda ash and sodium silicate. 

Experiments have proved that the disintegration of the printed 
papers with the detergent in kneaders where comparatively 
dry conditions are maintained produces poor results. The pig- 
ment is set free under such conditions that it is ground into 
the pores of the fibres and it is then almost impossible to wash 
out enough of it so that a good color can be obtained. If the 
papers are disintegrated and then diluted in the washer before 
mixing with the detergent much better stock will result because 
the separated ink is then in such a state that it tends to rise 
to the surface and can be more readily removed by the washers. 
It is evident, then, that a method of disintegration which tends 
to pull the ink from the surface of the paper is superior to one 
which tends to grind it into the fibres. 

Such a procedure has been embodied in the Winestock process 



OLD PAPERS 



91 



for the recovery of old papers. The apparatus used is shown in 
sectional view in Fig. 6 of a machine driven by a direct connected 
steam turbine, M. The essential features are a propeller tube 
B at the bottom of a cylindrical tank A which is mounted 
within a chamber H; through the horizontal part of the pro- 




Fig. 6. Westestock Defibering Machine 
Courtesy of Castle, Gottheil & Overton 

peller tube extends a shaft which turns at 2000 revolutions per 
minute and upon which are mounted two propellers of different 
pitch. Between the propellers is a baffle plate K to stop any 
inclination toward a rotary motion of the stock in the tube. 

The papers to be treated are opened up and dusted in a rail- 
road duster or its equivalent and then soaked in a tank of water 
at about 160 F. either with or without the addition of soda 
ash or other detergent. They are then charged into the cham- 



92 RAGS, ESPARTO, STRAW, BAMBOO 

ber H, together with any other additional detergents desired, 
such as a mixture of soda ash, caustic soda or a soap composed 
of tallow, soda ash, caustic potash and silicate of soda. The 
chamber H being full the stock overflows into the cylinder A 
and is circulated by the propellers back to the chamber H 
which it enters tangentially and through which it circulates to 
again enter A. The basic idea is that the paper suspended in 
water or a weak alkaline solution is struck by the blades at 
such a speed that it is unable to take up the rapid motion and 
is therefore pulled out or defibred while at the same time the 
ink is loosened from the fibres by the violent agitation. The 
second propeller has a greater pitch than the first so that there 
is cavitation between the two or a pressure on one side of each 
propeller and a suction on the other. The speed at which the 
stock circulates is estimated at 1200 ft. per minute. Since 
there is no cutting or grinding action in this machine there is 
no shortening of the fibres. 

The time of treatment necessary in this machine varies with 
the papers used and the products desired. Newspapers which 
are to be used for boards and from which the ink is not removed 
require only about fifteen minutes; if the product is to be used 
for white paper, and the ink must be washed out, about thirty 
minutes are required. Book and magazine papers need thirty- 
five to forty-five minutes' treatment and hard sized writings a 
somewhat longer time. The machine holds 700 to 900 lbs. of 
dry papers per charge and requires from 40 to 60 horse power. 

Assuming that the papers have been sorted with reasonable 
care and strings, bags and foreign materials eliminated, the 
Winestock process is suitable for all classes of papers, since the 
low temperatures and mild chemicals do not cause any serious 
discoloration of ground wood. As the apparatus liberates the 
ink and color from the fibres but does not remove the loosened 
pigment a subsequent washing is necessary. 



CHAPTER IV 
THE SODA PROCESS 

The principles upon which this process depends are the sol- 
vent power of the caustic soda for certain constituents of the 
wood and the hydrolysis of other constituents resulting, to a 
considerable extent, in the formation of products of an acid 
nature which are then brought into solution as salts of soda. 
Both of these processes neutralize the alkali and by diminishing 
its concentration and hydrolyzing power render it useless for 
further work until it is regenerated. The reactions and de- 
compositions involved are of a very complicated nature and 
the products are numerous and for the most part ill-defined 
and little understood. The degradation of the woody constit- 
uents is in general far greater than for the same constituents 
when dissolved by the sulphite process. 

Even at low temperatures alkali dissolves a very appreciable 
proportion of the non-cellulose constituents while if the tem- 
perature is raised the action is greatly intensified. Experiments 
on small poplar chips showed that a 3.3 per cent solution of 
caustic soda would dissolve 20.3 per cent of their weight by 
twenty-four hours' treatment at 25 C. while if the temperature 
were raised to 8o° C. the wood lost 31.6 per cent of its weight 
in the same time. Higher temperatures, such as are obtained 
by steaming under pressure, still further enhance the solvent 
power of the alkali and the speed with which it acts. 

In working with materials other than wood due consideration 
must be given to pectous substances. Working with bamboo 
Raitt * finds that pectose (matter soluble in 1 per cent NaOH 
solution at 100 degs.) is easily soluble in boiling NaOH solutions 

1 Indian Forest Records, Vol. Ill, part 3, "Bamboo as Material for Paper-pulp." 

93 



94 THE SODA PROCESS 

but that it gelatinizes at the temperatures employed in digestion 
and is therefore likely to become mechanically attached to the 
cellulose and is then very difficult to wash out. Pectose, fat 
and wax grouped together neutralize 0.32 per cent of NaOH on 
the raw material for each 1 per cent found on analysis. Lignin, 
unlike pectose, is not soluble in weak solutions nor at tempera- 
tures below 130 degs. 

The wood most used in the soda process is poplar, at least in 
the northern part of the United States, but because of its in- 
creasing cost and scarcity other woods are frequently substi- 
tuted. Among these may be mentioned basswood, maple, birch, 
cottonwood, tulip tree, sycamore, several kinds of gum, chest- 
nut, beech, etc. The best results are obtained if the different 
kinds are treated separately but this is frequently impossible 
without an excessive amount of labor. If mixed woods are 
used it is desirable to employ those which require about the 
same degree of treatment and to keep the mixture as nearly 
constant as possible. The mixing of woods which require 
widely different cooking conditions invariably means diminished 
yield because of the overtreatment of at least one kind in order 
that the most difficult to reduce may be sufficiently cooked. 

For long fibred stock, spruce, hemlock, pine and white fir are 
sometimes treated by the soda process. They require more 
alkali and longer cooking and yield less pulp than the broad- 
leaved woods. The soda pulp industry is, however, using pine 
in rapidly increasing quantities and in this way it is possible 
to use a number of woods which are too resinous to be treated 
by the sulphite process. According to the United States De- 
partment of Agriculture out of a total of 843,048 cords of wood 
used in the soda process during 1917, 379,466 cords were poplar, 
11,069 cords were hemlock, and 116,267 cords were pines of 
various kinds. 

On account of the vigorous action of the alkaline solutions 
less care is necessary in preparing the wood than for the sulphite 
process. Knots are either dissolved by the treatment or left 
in such condition that they are easily separated by the screens. 



THE SODA PROCESS 



95 



Contrary to the usual belief the inner bark, however, is a source 
of trouble and should be removed as completely as possible. 
It cooks with difficulty, uses up fully as much caustic soda as 
sound wood, and bleaches with far more difficulty than the 
fibre from the wood. If the two are cooked and bleached 
together the resulting product is liable to be contaminated 
with brown, stringy shives. The outer bark also uses up a 
large amount of caustic and in cooking breaks down into masses 
of cells which will not bleach to better than a yellowish brown 
color and hence cause dirt specks in the bleached pulp. These 
are not the only faults of bark, for its rough surface tends to 
catch dirt from outside sources, such as cinders, sand, etc., and 
transfer it to the pulp. 

It is not necessary to remove decayed portions of the wood 
since they are completely resolved during the cooking and do 
no harm unless they are of a very black nature. Such decayed 
wood, however, gives a very low yield of fibre and if present in 
large amount greatly reduces the output of the digesters, so 
that for this reason, at least, its use is to be avoided. The cellu- 
lose in partly decayed poplar wood was found by us to be 24.9 
and 27.0 per cent in two samples as compared with 63 per cent 
for sound wood. 

The wood is chipped by running the logs diagonally against 
the face of a rapidly revolving disc from which project from 
two to four knives. The distance to which these extend de- 
termines the length of the chip, which for poplar is from three- 
quarters of an inch to an inch and a quarter. The chips go 
next to some form, of screen which separates them into three 
grades, dirt and very fine material, good chips, and slivers and 
coarse pieces. The dirt and fine stuff is waste, so far as pulp 
making is concerned, though it is often used as fuel in the boiler 
house, while the slivers and coarse pieces are either crushed or 
rechipped and returned to the screens. Uniformity of cooking 
is greatly aided by a uniform size of chips but it is not so essen- 
tial as in the sulphite process because of the greater penetrating 
power of the alkaline liquor. 






Fig. 7. Vertical Digester, Section Showing Inlets, Pump, and Piping 
(96) ^ 



DIGESTERS 



97 



The digesters used in this process are of the usual rotary or 
stationary types but vary greatly in size and capacity. The 
tendency is toward the vertical stationary type Fig. 7, and away 
from the rotaries since the former effect savings in floor space, 
power required and time of filling and emptying. The latter is a 
very appreciable item, as a rotary holding 3 to 3! cords requires 
three hours for blowing down pressure, discharging the contents 
and refilling with chips and liquor, while a vertical digester 



A. Digester 

B. Heater for cook- 

ing liquor 
C Strainer 

D. Boiler to supply 

steam to B 

E. Pump to return 

condensed 
water to boiler 




W/^//»: ,.',.,::? 



Fig. 8. Morterud Digester 



holding 14 to 15 cords of wood requires only one hour for the 
equivalent operations. The size of rotary digesters in American 
practice is generally about 20 X 7 ft., while the vertical digesters 
range from 27 to 49 ft. tall by 7 to 10 ft. in diameter; one 30 X 8 
ft. will hold about 5.5 cords while one 49 X 10 ft. will hold 
nearly 15 cords of wood. 

A modified type of digester is that used in the Morterud 
system of cooking with forced circulation and indirect heating. 
Such an outfit is shown in Fig. 8. The steam in this system 
is not blown directly into the charge but the liquor is circulated 
through an outside exchange heater in which steam is the source 



98 THE SODA PROCESS 

of heat. The condensed steam is returned to the boiler as feed 
water under high pressure and at a high temperature. The 
claims for this process are savings in coal and alkali and an 
increased yield because of the more even temperature of the 
cooking liquor. 

Another modification is that of the jacketed digester in which 
the steam for heating is between the two walls. Experience has 
proved that these are very hard to keep tight as the stays be- 
tween the walls cause very frequent leaks. No insulating cov- 
ering can therefore be used and the steam consumption is very 
high because of the great loss by radiation. 

The material of the digesters is either iron or steel and they 
are made either riveted or welded. The latter is much to be 
preferred, since" the alkaline solutions work their way through 
crevices which would be impervious to water and for this reason 
a riveted seam is very difficult to make perfectly tight. As the 
alkaline solutions are practically without action on the material 
of the digester no lining is necessary. 

In filling the digester the chips and liquor are run in at the 
same time and in order to get in as large a charge as possible 
a tamping device is sometimes employed. This is especially 
necessary for horizontal rotaries. The time required for charg- 
ing a rotary holding 3 to 3I cords is about one hour, while chips 
from 14 to 15 cords of wood can be run into a vertical digester 
in 1 5 to 20 minutes. 

The cooking liquor for the soda process is merely a solution 
of caustic soda containing a small amount of sodium carbonate. 
It is generally made at the mill by causticizing soda ash with 
quick lime. The reaction on which the process depends is 
Na 2 C0 3 + CaO + H 2 = 2 NaOH + CaC0 3 . 

This is a reversible reaction and the extent to which the soda 
ash is causticized depends on the dilution of the liquor. Ex- 
periments by Lunge 1 illustrate the effect of concentration as 
follows: 

1 Lunge: Sulphuric Acid and Alkali, 2nd ed., Vol. II, p. 750. 



CAUSTICIZING 



99 



Liquor before causticizing 


After causticizing 


Per cent Na2C0 3 


Specific gravity 


Per cent causticity 


2 

5 
IO 

14 

20 


i .022 at 15 C. 
i .052 at 15 C. 
1. 107 at 15 ° C. 
1. 150 at 15 C. 
1. 215 at 30 ° C. 


99-4 
99.0 
97.2 

94-5 

90.7 



It is obvious that the lower the concentration the higher the 
causticity and that therefore a demand for a definite concen- 
tration sets a limit to the causticity attainable. Attempts to 
increase the causticity by boiling either under diminished or 
increased pressure have met with no success; practically all 
causticizing is therefore done in tanks under atmospheric 
pressure. 

The type of equipment used for causticizing varies greatly 
in the different mills; it may be stated to consist generally of 
a wrought iron tank fitted with an agitator and frequently a 
perforated basket near the top for holding the lime. The tank 
is filled with soda ash solution until the bottom of the basket is 
just covered; it is then brought to a boil and the lime added to 
.the basket very gradually. As the lime slakes it passes through 
the perforations while stones or unburned cores are retained 
and may be easily removed. If the tank is not fitted with a 
basket the lime is thrown directly into the hot soda ash solution 
and slaked in the bottom of the tank. It has been found best 
to boil with a steam coil rather than by blowing steam directly 
into the liquor. Agitation with compressed air is also not to 
be recommended as it reduces the causticity slightly. The time 
of boiling has a considerable influence on the causticity obtained 
as the latter increases with the duration of the boil. The size 
of the plant in relation to the necessary output frequently 
limits the time of boiling but if possible it should be continued 
for at least an hour; beyond this point it is doubtful if the 
gain in causticity will pay for the extra expense. 



IOO THE SODA PROCESS 

Greater causticity can also be obtained in many cases by in- 
creasing the agitation. This has been done in certain instances, 
where adding more wings to the agitator shaft, or increasing its 
speed, has enabled less lime to be used in obtaining the same 
amount of caustic soda. Tests on a small scale have proved 
that thorough agitation is to a large extent equivalent to boil- 
ing, and that if the agitation is complete enough the charge 
need not be boiled at all as a temperature of 85 degs. is ample. 

The causticizing operation is generally carried out in about 
the following manner. The soda ash and lime are boiled and 
then allowed to settle in the same tank. The clear liquor is 
drawn off by an adjustable syphon, more soda ash and water 
are added and the sludge again boiled up and then pumped 
over into a second tank. The sludge from this is flooded with 
weak liquor and again boiled up and settled. Fourth and fifth 
boilings are made with clear water. The clear liquors from the 
first four boilings combined make the cooking liquor, while the 
fifth boiling produces the weak liquor for a subsequent third 
boil. 

The Dorr Company have recently proposed to causticize 
and wash the lime mud in a continuous operation by machinery 
similar to that used in metallurgical work. The lime is crushed 
and continuously mixed in definite proportions with a soda 
ash solution; the mixture then passes through three reaction 
agitators which are furnished with steam coils and then goes 
to the first thickener. The clear liquor overflowing from this 
goes to the storage tank for cooking liquor, while the sludge is 
pumped to the second thickener where it is mixed with the 
overflow from a third thickener. The clear liquor from the 
second thickener flows to the reaction agitators, while the sludge 
goes to the third thickener and thence to waste or to a recovery 
plant for lime. A causticizing plant of this type is shown in 
plan in Fig. 9. A plant operated in this manner has been in 
operation for some time and is said to be giving good satisfac- 
tion. It seems doubtful if it is very much superior to a carefully 
supervised plant of the ordinary type. 




< 

Ph 

O 
g 



u 



u 



O => 



o 



PM 



(101) 



102 THE SODA PROCESS 

The lime mud produced in causticizing is generally a waste 
product, though there is sometimes a small local demand for 
agricultural purposes. Attempts have been made to reburn 
the mud and use the lime over again and a number of plants 
are now operating with rotary kilns similar to those used in the 
cement industry. The lime mud is freed from water as much 
as possible by mechanical means and then enters the kiln, 
through which it passes in a direction opposite to the combus- 
tion gases. It is first dried and then heated to such a tempera- 
ture that the carbon dioxide is driven off and the material 
delivered as burned lime. A kiln 7 ft. in diameter and 120 ft. 
long will burn 35 to 40 tons of lime per day, while for capacities 
between 20 and 30 tons a kiln 6 ft. by 100 ft. is sufficient. If 
the mud enters at 55 per cent dry, the fuel requirements will 
be about 9500 cu. ft. of natural gas or 675 lbs. of coal per ton 
of lime burned. 

In order to keep the impurities down to a reasonable figure 
it has been found necessary to remove about 10 per cent from 
the circuit regularly. Where producer gas is used one passage 
through the kiln adds three pounds of impurities for every 
100 lbs. of quick lime, but this only reduces the causticizing 
power of the lime 2 per cent because the impurities are held 
mechanically rather than chemically. When powdered coal is 
used instead of gas 6 per cent of impurity is added and this 
reduces the causticizing power of the reclaimed lime by fully 
18 per cent. The lime mud and the reclaimed lime from a gas- 
fired kiln contain the following impurities for every 100 lbs. of 
available calcium oxide; as may be seen nearly all of the im- 
purities added in reclaiming come from the fire brick lining. 



Magnesia, MgO 

Oxides of iron and alumina, Fe203 and AI2O3. 

Sodium oxide, Na 2 

Sulphur trioxide, SO3 

Silica, Si02 



Lime mud 


Reclaimed 
lime 


Per cent 


Per cent 


1-3 
0.9 
1.6 


1 .1 
2.6 
1 .1 


0.2 


0.7 


Q-7 

4-7 


2.2 

7^7 



COOKING 



103 



The following analyses show the composition of the new lime 
and the recovered lime from a plant using natural gas as a fuel. 



Calcium carbonate, CaCOs 

Iron and alumina, Fe 2 Os and AI2O3 

Silica, Si0 2 

Calcium oxide, CaO. . . 

Magnesia, MgO. . . ; 

Undetermined 



New lime 


Recovered 
lime 


Per cent 


Per cent 


4.48 
0.15 


3-91 
1 .62 


0.16 

92.00 

2.62 

0.59 


0.70 

89.58 

1.96 

2.23 



The recovered lime is in the form of rounded nodules ranging 
up to the size of a hen's egg. It is often slightly greenish or 
yellowish in color and slakes rather more slowly than good 
lime. 

The strength of the caustic liquor used in cooking varies 
from 8° to 15 Be. at 6o° F. according to operating conditions. 
Stationary digesters require more dilute solutions than rotaries, 
while wet wood necessitates increasing the strength of solution 
to counterbalance the water contained in the chips. If digesters 
are heated by jackets or closed coils, weaker liquors may be 
used because they are not diluted by any condensed steam. 
With direct heat in rotaries about 700 to 900 gals, of liquor 
are used per cord of wood while in digesters the liquor amounts 
to about 800 to 1 100 gals, per cord. 

The boiling operation is a very simple one, the object being 
to reach full pressure as soon as possible and maintain it to 
the end of the cook. During this period the air which collects 
in the top of the digester is blown off several times through 
the " relief pipe" so that no false pressure may be recorded on 
the gauges. This " relief " is usually not necessary when cooking 
in rotary digesters. The uniformity of the cook depends on 
good circulation of the liquor and in practice this is obtained 
in several ways. Some digesters are fitted with internal circu- 
lating pipes on the same principle as the vomiting pipes in rag 
boilers, while another very successful and positive method of 



io4 



THE SODA PROCESS 



circulating is to take the liquor from below the false bottom 
and pump it up into the top of the digester; as both sides of the 
pump are under the same pressure very little power is required. 
The steam consumed in cooking depends on the form of the 
digester, on whether it is covered with an insulating covering 
or not, and on the size of the charge. Steaming may be con- 
sidered as taking place in two stages, the period in which the 
charge is being brought up to pressure, during which the de- 
mand for steam is very great, and the period at full pressure 
when only enough steam is required to make up for the heat 
lost by radiation. Records obtained with steam flow meters on 
three sizes of digester gave the following results in pounds of 
steam required. 



While coming up to pressure (lbs. per hr.) 
During period at pressure (lbs. per hr.) . 
Total required during cook (lbs.) 



3 -cord rotary 



7,500-7,800 

500 

12,125 



6J-cord 

rotary 



10,800 

1,050 

19,360 



15-cord vertical 
digester 



20,000-22,100 

1,250* 
37.750-44-250 



* Calculated by radiation formula for steam pipes. 

In spite of the apparent simplicity of the process there are a 
number of factors which greatly influence the results, and uni- 
form and satisfactory cooking depends on the proper adjust- 
ment of these variables. Much study has been given to these 
factors by the author and at about the same time by the Forest 
Products Laboratory who published a bulletin 1 on their re- 
sults. The following discussion of the individual variables is 
based on the author's experiments which were very carefully 
made in special apparatus which enabled very close control of 
all conditions to be maintained. The experiments were all 
made with poplar chips and all yields are figured as bone dry 
fibre on bone dry wood. Fig. 10 illustrates the effect of changes 
in steam pressure upon the yield and the bleaching properties 
of the fibre when all other cooking conditions are kept constant. 

1 U. S. Dept. of Agriculture, Bulletin No. 80. 



*T 



STEAM PRESSURE 



i°5 



In this and the succeeding charts the fibres were all bleached 
to a standard color so that the figures are directly comparable. 
It is at once evident that the yield is greatly influenced by the 
steam pressure employed and that the decrease in yield is at a 
nearly constant rate for pressures between 70 and 130 lbs. 
Throughout this range increasing the steam pressure 10 lbs. 































Per cent Bleach 
6 7 8 9 


130 














































































































































CO 




































O 

On 




































g 




































CO 

CD 
<H 

Ph 




































1 
I 90 














































































































































70 





































34 



36 



38 



40 42 
Per cent Yield 

Fig. 10. 



44 



46 



decreases the yield by about 2 per cent on the absolutely dry 
wood used. The bleach required is practically constant, prov- 
ing that even 70 lbs. steam pressure will produce satisfactory 
pulp. This is contrary to the claims of Christiansen x who 
states that the minimum temperature for the production of 
soda pulp is 170 to 175 C. (100 to 115 lbs. steam pressure). 
Probably this discrepancy is to be accounted for by the differ- 
ence in the woods used. 



Christiansen: Natronzellstoff, Berlin, 19 13. 



io6 



THE SODA PROCESS 



A study of the effect of steam pressure in semi-commercial 
cooks (400 lbs. chips) in a vertical, stationary digester gave 
results following very closely the form of curve of the small- 
scale cooks. The yields were, however, 8 to 9 per cent 



LUU 














































































80 






































































































60 


» 




































































































/in 



























•33 



35 .37 

Per cent yield 

Fig. 11. 



39 



41 



43 



greater, which appears to be a characteristic difference between 
the vertical digester and the small rotary heated by a gas 
flame. 

The influence of the initial concentration of caustic soda in 
the cooking liquor is shown in Fig. 11. Decreasing the con- 
centration increases the yield slightly but this factor is evidently 
of less importance than the steam pressure since increasing 



SODA ADDED 



107 



from 80 to 100 grams per liter reduces the yield only about 
1.4 per cent. 

Fig. 1 2 shows the variation in yield and bleach required with 
changes in the per cent of caustic soda added. With 22 per cent 
of caustic the yield was high but the fibre was unsatisfactory 



50 


































46 


































































42 


































































■a 

■d 

* 38 

£ 
O 












































Yiel 


I 




















fl 34 



































u 


































P-l 

30 






































\b 


each 


























26 




































































22 






































2 


1 


2 


8 


3 


2 


3 


6 


4 





4 


4 


4 


8 





11 



Per cent Yield 

15 19 

Per cent Bleach 

Fig. 12. 



23 



27 



31 



in that it was commercially unreachable. Increasing the caus- 
tic to 28 per cent decreased the yield very greatly but produced 
easy bleaching fibre. When the caustic is brought up to 40 to 
50 per cent of the weight of wood the form of curve suggests 
that its maximum cooking effect is nearly reached. This curve 
shows why 25 per cent of caustic soda is the most satisfactory 
for commercial work since if more is used the yield is too greatly 
reduced while if much less is employed the bleach required 



io8 



THE SODA PROCESS 



increases to an excessive amount. Evidently the percentage of 
caustic soda is one of the most important points to watch in 
the control of the soda process. 

The influence of time under pressure is shown in Fig. 13, 
where cooks ranging from three to nine hours are recorded. The 
rate of decrease in yield is not the same for equal intervals of 

























Per cent Bleacfi 
5 6 7 8 




9 




1 


































































































































7 

03 
U 


































































O 


































a 


























1 








5 






































































































































3 



































35 



37 



39 41 

Per cent Yield 

Fig. 13. 



43 



time for an increase from three to five hours causes a greater 
diminution in yield than an increase from seven to nine hours. 
Considering the questions of yield and bleach required the 
time factor is of much less importance than either the steam 
pressure or the amount of caustic added. 

To bring these charts onto a common basis the table below 
has been calculated to show what changes in the variable cook- 
ing factors will cause a decrease of 1 per cent in the yield ob- 



CAUSTICITY 



109 



tained, considering in each case the entire range covered in the 
study of the particular variable. For comparison the results 
of experiments of the U. S. Forest Service * are also given. 



Decrease in yield of 1 per cent caused by 


According to experiments by 


The author 


U. S. Forest Service 


Increase of NaOH used by 


i . 3 per cent 
1 . 2 hours 
5 .0 lbs. 
10. gms. per liter 


2 per cent 


Increase of time by 


Increase of steam pressure by 

Increase of concentration by 


5 lbs. 
13 gms. per liter 



The condition of the wood, whether very wet or very dry, is 
of importance in adjusting the strength of the cooking liquor as 
already mentioned. The chief point to be watched is the final 
concentration of the caustic soda, taking into account the moist- 
ure in the wood as well as that in the liquor itself. Experi- 
ments have shown that if this ultimate concentration is kept 
constant the same yield will be obtained whether the chips 
contain 3 per cent or 22 per cent of moisture. 

The causticity of the cooking liquor is another factor which 
is supposed to have a large influence on the cooking process. 
This is probably true in mills where the strength of the cooking 
liquor is regulated by the hydrometer test or by the titration 
for total alkali. If the volume to be added is based on either 
of these tests the actual caustic soda added may not be enough 
to cook the wood thoroughly and the low causticity will at 
once be blamed. As a matter of fact it makes no difference in 
the yield or bleaching properties of the fibre whether the caus- 
ticity is 80 or 99 per cent provided liquor enough is present to 
supply the correct amount of actual caustic soda. This is also 
true of salt, which is sometimes present because of the use of 
electrolytic caustic, or may even be added intentionally with 
the idea of protecting the fibre and increasing the yield. 

It is of course true that the causticity of the cooking liquor 

1 U. S. Dept. of Agriculture, Bulletin No. 80. 



IIO THE SODA PROCESS 

has a considerable effect upon the economy of the cooking and 
recovery processes since the carbonate is carried through the 
system as so much inert material which must be handled by 
the evaporators and black ash burners and is subjected to a 
loss of 10 to 20 per cent during each cycle. It has been esti- 
mated that in a plant making 70 tons of fibre per day, each 
increase of 1 per cent in causticity means an annual saving of 
about $500. 

In diluting the liquor to the proper strength for use it is the 
custom of some mills to add a certain proportion of black liquor. 
This is done with the idea of more completely utilizing the 
alkali in the black liquor and of obtaining a more concentrated 
liquor to go to the recovery system. As it is in direct line 
with the production of brown "kraft" fibre it is logical to ex- 
pect that the bleaching properties of the fibre would suffer, 
and this has been found to be actually the case where black 
liquor has been added to the charge for cooking poplar. If 
8 per cent of the total liquor consists of black liquor the bleach 
required is found to increase from 8.4 to 10. 1 per cent, while if 
17 per cent of black liquor is added the fibre requires 14. 1 
per cent of bleach. If no fresh liquor is used, but the entire 
charge is made up of black liquor brought to the correct strength 
by adding solid caustic soda, the fibre produced requires at least 
22 per cent of bleach. While the bleaching properties of the 
fibre suffer, the yield of unbleached fibre is increased by about 
3 to 4 per cent by the use of 8 to 17 per cent of black liquor. 

The study of the time factor in cooking immediately brings 
up the question of how rapidly the reaction between the wood 
and the caustic soda takes place. Fortunately this reaction 
can be followed very readily by means of analyses of the black 
liquor. If the causticity of the liquor as added is known the 
consumption of caustic soda may be calculated at any time 
from the black liquor analysis by means of the following formula: 



RATE OF REACTION 



III 



where X = per cent NaOH used up, based on the bone dry 
wood, 
A = per cent causticity at the start, 
B = per cent causticity at time of sampling black liquor, 
C = per cent NaOH added on bone dry wood. 

Fig. 14 shows graphically the results of three such studies 
on poplar wood. Curve A was obtained from a vertical sta- 
tionary digester holding 400 lbs. of wood, B is from a rotary 
digester holding about 3 cords, while C is from a vertical sta- 




3 4 

Time in Hours 

Fig. 14. 

tionary digester of a capacity of 14.5 cords of wood. All three 
cooks were made at no lbs. steam pressure and the ratio of 
wood to alkali was the same for all. In each case the percent- 
age of caustic soda consumed is based on the bone dry wood 
used. The weight of wood used in the largest digester was 
estimated from the average weight of a cord of poplar, but in 
the other two cooks the chips were accurately weighed; this 
may have introduced a slight error into curve C but this would 
merely alter its position on the chart and would not change 
its form. 



112 THE SODA PROCESS 

These curves are characteristic of the soda process. The 
difference between small and large cooks is probably due to 
the difference in the speed with which they heat up, and in 
fact by forcing the steaming in the rotary digester it has been 
found possible to make the curve almost exactly duplicate 
curve A both in form and position. They also explain why 
•the time factor is one of minor importance, for the reaction is 
one of such great rapidity that over half of the total alkali 
consumed in a seven-hour cook is used up during the first hour, 
in spite of the fact that during the whole, or a great part, of 
this time the charge is being brought up to full pressure. 

Tests on Engelmann spruce and red alder have given results 
which practically duplicate the curves of Fig. 14, while Heuser * 
working on beech wood obtained very similar results. Chris- 
tiansen, 2 on the other hand, claims to have established the fact 
that there are points at which the reaction ceases for a while 
and then begins again. These pauses are of different duration 
and take place sooner or later in the cook according to local 
conditions. Some of his cooks show two such pauses, some 
one and some not any, and a careful study of his work leads to 
the conclusion that they are probably due to inaccuracies in 
the methods which he used in sampling and analyzing the 
black liquors. It does not seem reasonable that the reaction 
should cease for a period of half an hour and then begin again 
and the author has been unable to find in the work on poplar 
any trace of such pause which was not readily explained by the 
difficulty of obtaining representative samples from the black 
liquor in the digester. 

The methods of analysis used in determining the rate of reac- 
tion make possible also a study of the relationship between the 
caustic soda consumed and the yield of fibre produced. This was 
investigated by us and the results published 3 in 191 2 and from this 
paper the curves for spruce and poplar in Fig. 15 are repro- 

1 Heuser: Wochbl. Papierfabr., 44, 2209. 

2 Christiansen: Uber Natronzellstoff. 

3 Communications: Eighth International Cong, of Appd. Chem., XIII, p. 265. 



SODA CONSUMPTION AND YIELD 



"3 



duced. It appears from this that up to the point where 14 
per cent of caustic soda is consumed there is merely a softening 
of the chips and almost no separation into fibres; between 14 
and 19.5 per cent consumption seems to be the critical stage, for 
between these points the transition from chips, through shives 
to commercially satisfactory fibre takes place. Beyond a con- 
sumption of 19 per cent the action appears to be almost en- 



28 
26 
24 
22 
20 
18 
16 
14 
12 
10 
8 

e; 

4 

2 










S 










































\ 














CHART A. 


































































OWN 


































































3 

03 

a 


















O^ 


-Po] 


jlar 





































# 


o\. 




































Spr 


uce 






o^ 1 


















fc 










































a 























































































_ 














































































































Vd 














































) 


1 





2 





3 





.4 



P( 


5 
jrcei 



ltT 


6 
otal 



Yie 


7 
Id 





8 





3 





100 



Fig. 15. 



tirely a destruction of the cellulose and the decrease in yield 
bears a constant ratio to the increase in caustic consumption. 
The results from cooks of spruce chips give a very similar curve 
but the yield for a given consumption of caustic soda is con- 
siderably lower than for poplar as might be expected from a 
knowledge of the composition of the two woods. Studies along 
this same line by the U. S. Forest Service x gave results which 
seem to indicate that high consumption of caustic soda 



22 



U. S. Dept. of Agriculture, Bulletin No. 80. 



ii4 



THE SODA PROCESS 



per cent or more on the weight of the wood — may be obtained 
without much lowering of the yield. We believe that this 
difference may be due in small part to differences in the appara- 
tus and wood used but that by far the greater part of it is caused 
by the analytical methods used by the Forest Service which 
take no account of the occlusion of caustic soda in the precipi- 
tate caused by barium chloride. It is highly probable that this 
method of investigation could be worked up into a good con- 
trol test which would largely eliminate over- or under-cooked 
soda fibre and would tell with reasonable accuracy when the 
desired quality of fibre had been produced. 

Actual mill results in the cooking of some Canadian woods 
are given by De Cew : as follows: 



Wood 



Black spruce (Picea nigra) . . 
Hemlock (Tsuga canadensis) 
Poplar (P. grandidentata) . . . 

Bass (Tilia americana) 

Birch (Betula alba) 

Birch (Betula lutea) 

Maple (Acer rubrum) 



Specific 
gravity 



0.41 

0.42 

o.43 
0.425 
0.58 . 
0.66 
0.64 



Weight 
per 
cord, 
lbs. 



2250 
2300 
235° 
2325 
3190 
3630 
3520 



Soda 

as 

Na 2 C0 3 



900 
950 
800 
800 
800 
.850 
850 



Yield 



Per 

cent 



40 
38 
44 
44 
42 
40 
40 



Air dry 
fibre per 
cord, lbs. 



IOOO 

970 

1 150 

II3S 
1490 
1610 
1560 



From other reliable sources the following data have been 
collected: 



Wood used 


Weight per cord 
bone dry 


Alkali per cord 
as Na2C0 3 


Yield air dry fibre 
per cord 


White maple 

White birch 

Gum and poplar 

Poplar 

Gum 


2970 

3091-3218 

3268 

255° 
2976-3040 


900 

1035-1120 

1022 

760 

920-1138 


1520 
1460-1592 

1160 

1250 
I 2 15-1432 





From soda mill records of the cords of wood cooked and the 
new soda ash added to replace losses it appears that 184 lbs. of 

1 De Cew: J. Soc. Chem. Ind., 1907, 561. 



V 



MODIFIED PROCESSES 115 

soda ash per cord suffices for poplar when the recovery is 76 
per cent, or 153 lbs. with a recovery of 87.5 per cent. For a 
mixture of 60 per cent gum and 40 per cent poplar, used during 
a period of six months, 157 lbs. fresh soda ash per cord was 
found to be enough when the recovery was 85.7 per cent. 

The best modern mills are able to cook deciduous woods in 
about four hours and coniferous woods in six hours. The success 
of these short cooks depends very largely on vigorous circula- 
tion and a rapid supply of steam. By removing air from the 
chips and using superheated steam quicker penetration of the 
liquor is obtained, which also hastens the cooking. 

It has been proposed at various times to modify the regular 
soda process by the addition of small amounts of other chemi- 
cals such as salt, sodium nitrate, etc., and Schacht 1 even rec- 
ommends cooking with a liquor consisting largely of sodium sul- 
phite and thiosulphate and containing only enough caustic soda 
to dissolve silica and aluminates. Careful tests have failed to 
show that salt, even when used to the extent of 15 per cent of 
the weight of the wood, exerts any protective action and its 
presence does not appear to increase the yield. Another modi- 
fication is that of Freeman who proposes to carry out the cook- 
ing in a reducing atmosphere obtained by passing hydrogen 
through the digester until all air is expelled. Still another 
variation consists in saturating the chips with cooking liquor 
under pressure, drawing off the excess and completing the cook 
by steaming as usual. This is claimed to give greater yield 
and better fibre because of the more uniform treatment of the 
chips. 

The most recent proposal is to add a very small amount of 
sulphur — about 0.2 per cent on the weight of the wood — to 
the alkali during causticizing and it is claimed that this will 
materially increase the yield without causing a serious nuisance 
by its odor. Very careful small-scale tests of this modification 
have proved that woods vary in their response to the presence of 

1 Schacht: Papier Ztg., 1901, 26, 3143. 



n6 



THE SODA PROCESS 



sulphur; some give a larger yield while some do not, but in 
no case is the claim for 10 per cent greater yield justified. The 
fibre produced in the cooks containing sulphur bleaches more 
easily in every instance. The average yield's for this series of 
tests are tabulated below: 



Kind of wood 



Percentage yield on bone dry basis 



Without 


sulphur 


38 


9 


36 


8 


40 


9 


40 


6 


41 


7 



With 0.2 per cent of 
sulphur 



Poplar 

Spruce 

White birch. 
White maple 
Tulip tree. . 



41.9 

35-7 
40.9 
41.4 
42.6 



It is evident that each kind of wood must be tested sepa- 
rately as the use of sulphur is not equally beneficial in all cases. 
It is probably due to this reason, as well as to the difficulty of 
determining yields in actual mill operations, that at least two 
mills where the use of sulphur has been tried out during a period 
of several months report that no increase in yield or other ad- 
vantage can be noted and that it tends to produce bad odors 
even when used in such small amounts as 0.2 per cent on the 
weight of the wood. 

Numerous other modifications of the soda process have been 
proposed from time to time, among which may be mentioned 
Drewsen's 1 plan for boiling wood chips in a liquor obtained 
by adding 10 per cent of quicklime and 2 to 4 per cent of sul- 
phur to water; the fibre is finally boiled with sodium carbonate 
to remove all sulphur. Lee 2 proposes, in the case of flax waste, 
boiling in a 3 per cent solution of saccharate of lime. Burton 3 
combines a mechanical treatment with the soda process by 
cooking in drums furnished inside with loose rollers of steel or 
of steel filled with lead. This is somewhat similar to the 
Muntzing method of treatment 4 in which the logs are placed 



1 U. S. Pat. 996,225, Jan. 27, 1911. 
3 Ger. Pat. 226,912, Apr. 1, 1909. 



2 U. S. Pat. 713, 116, Nov. 11, 1902. 
4 Paper, Jan. 20, 1915, p. 15. 



ALCOHOL IN RELIEF 



117 



in the rotary digester without chipping and by their rubbing 
action quickly separate the fibres. These are rapidly removed 
from the sphere of action of the liquor by pumping the latter 
through a filter press from which the clear liquor is returned to 
the digester to continue its work. Notably larger yields are 
claimed for this process. 

In the case of woods rich in turpentine and rosin much study 
has been given to the possibility of recovering these, while at 
the same time utilizing the wood as a source of fibre. The 
turpentine can be obtained without difficulty in the blow-off 
from the digesters. By a partial cook, followed by a salting 
out of the liquor with more caustic soda, Bates 1 has shown 
that it is possible to recover much -of the rosin in the form of 
sodium resinate. Similar investigations have been conducted 
by Veitch and Merrill 2 and the patents of Saylor, 3 Aktchourine, 4 
and Williamson 5 are based on practically the same principles. 
The importance of such problems is strongly emphasized by 
the estimate of the U. S. Government that there are 21,000,000 
cords of waste resinous woods in the South annually. 

The blow-off from the digesters also contains, besides tur- 
pentine, other materials of an easily volatile nature. From the 
relief of poplar cooks there have been condensed a small amount 
of oil and a liquid containing aldehydes, ketones, alcohol, ace- 
tone, etc. From small scale cooks Bergstrom has obtained the 
following yields of alcohol based on the dry wood used. 

Per cent 

Fichte (Picea excelsa) 0- 67 

Kiefer (Pinus silvestris) 0.67 

Pinus palustris 53 

Pinus echinata 55 

Aspen (Populus tremuloides) ' 0.67 

Birch (Betula alba) Q _g I 

Gum (Eucalyptus) , 83 

1 Bates: Dissertation, Columbia University, 19 14. 

2 Veitch and Merrill: Bureau of Chem., Bull. No. 159. 

3 Saylor: Fr. Pat. 428,678, April 19, 1911. 

4 Aktchourine: Fr. Pat. 433,424, Aug. n, 1911. 

5 Williamson: U. S. Pat. 1,025,356, May 7, 1912. 



u8 



THE SODA PROCESS 



At the completion of a cook the contents of a rotary digester 
consists of material thoroughly reduced to the fibrous condi- 
tion while that in the stationary digester still retains very 
largely the shape of the original chips. Rotary digesters are 
discharged by blowing off pressure until the heads can be re- 



Baffle 




-Discharge Pipe 
Fig. 16. Blow Tank or Separator 

moved and then emptying the contents by revolving the digester. 
Vertical digesters are emptied by blowing the entire charge 
under full pressure through a pipe leading from the bottom of 
the digester to a blow pit or some form of steam separator. A 
very satisfactory device of this sort is shown in Fig. 16. The 
stock enters tangentially at such high speed that it hugs the 



y 



WASH PITS 



119 



wall of the separator while the steam escapes to the center and 
out through the ventilator. On blowing the charge the sud- 
den release of pressure causes violent evolution of steam from 
the moisture in the chips and this, together with the mechanical 
action of passing through the discharge pipe, causes complete 
disintegration into the fibrous state. 

The blowing of a digester causes a very large waste of steam. 
It has been estimated that in blowing a 15.6-cord digester there 
escape into the atmosphere 34,400 lbs. of steam within a period 
of about 15 minutes. This represents about 41,200,000 British 
thermal units and at atmospheric pressure it would occupy a 
volume of 925,000 cu. ft. The cost of constructing an exchange 
heater which would handle this enormous volume of steam in 
such a short time has hitherto been considered prohibitive, and 
very few attempts have been made to stop this waste. 

From the separator the stock drops by gravity to the wash 
pits. At this point it contains the fibre, all the alkali originally 
added, the organic matter dissolved during the cook and a 
large amount of water both from the liquor added and from 
the condensed steam. The composition of three samples taken 
during the entire time of discharge was found to be as follows: 



Fibre (bone dry) 

Alkali as Na 2 

Organic matter and C0 2 
Water 



No. 1 



Per cent 

11.38 

4.14 

10.76 

73-72 



No. 2 



Per cent 

8.15 

4.06 

II. 31 

76.48 



No. 3 



Per cent 

7-32 

2.92 

8.24 

81.51 



The wash pits are iron tanks with perforated false bottoms; 
they are of various sizes and shapes but each should be of suffi- 
cient capacity to hold the entire charge of a digester with room 
above the stock to allow for flooding with water. The pits 
supplied in one mill for digesters of about 15 cords capacity 
are 19 ft. 6 ins. in diameter by about 13 ft. deep above the 
false bottom which has a 2-in. pitch toward the central outlet 
to aid in washing out the stock. One digester charge fills 



120 



THE SODA PROCESS 



one of these wash pits to a depth of about 9 to 10 ft. when 
leveled off. In another mill rectangular tanks are recommended, 
the size for 5200 to 5300 lbs. of pulp being 18 X 16 X 5 ft. 
deep. 

The charge is washed first by flooding with weak liquor from 
a previous wash; the liquor taken off during this period goes 
to the recovery plant. The next washing is with hot water, 
which produces the weak liquor used in the first flooding of a 
subsequent cook, and the final washing is with hot water which 
runs to the sewer as it is too weak to pay for evaporation. The 
approximate washing data for the 19^-ft. tanks mentioned above 
are as follows: 



Time of washing, hours 

Volume of liquor taken off, gals. 
Baume at end 



First wash 



4-7 
18,000-19,000 
5 at 70 C. 



Second wash 



5-8 

19,000-20,000 
o° at 50° C. 



Third wash 



2-3 



The net total washing time is thus eleven to eighteen hours 
per charge and the recovery of soda during the washing has 
been found to be about 98.5 per cent. The strong black liquor 
obtained by this method contains about 0.63 to 0.65 lb. of 
soda per gallon. 

In some mills the weak liquor is collected in a tank before 
being pumped on to the next pit, while in other mills using the 
so-called "cycle system" it is pumped directly from one wash 
pit to another. The advantage of the cycle system is that it 
requires less space and produces stronger liquor, while its chief 
disadvantages are that it requires more time to complete a 
wash and it is often necessary to hold a pit with the black liquor 
on it to the detriment of its bleaching properties. Spence * 
states that with hardwoods the liquor discharged from the 
digesters tests 12 Be. at 6o° F., while that going to the evapo- 
rators tests 9 Be. If the cycle system is used the liquor to the 

1 Spence: Paper, 25 (1919), 134. 



V 



WASHING BLACK STOCK 121 

evaporators would test ioj° Be. instead of 9 degs., this differ- 
ence being equivalent to a saving in evaporation of 46,000 
gals, per day for a plant with a daily capacity of 100 tons of 
pulp. 

The washing time depends very largely on the depth of stock 
which the wash water has to penetrate. By dividing the digester 
charge between two wash pits the time of washing can be very 
greatly reduced, but a weaker liquor is obtained and the re- 
covery is not so complete unless a much larger volume of liquor 
is collected. This is equivalent to saying that the greater the 
drainage area allowed per ton of fibre per day the more rapid 
will be the washing. Beveridge * mentions installations where 
this has varied from 7^ to io T \ sq. ft. but considers this far too 
little and recommends 35 sq. ft. for poplar and 45 to 50 for 
chestnut. The kind of wood used and the nature of the cook 
have an influence on the speed of draining; hardwoods drain 
slower than northern poplar and overcooking causes the fibre 
to be sufficiently gelatinous to drain slower than a normal 
cook. 

The temperature of the water used also influences the speed 
of washing, hot water penetrating the stock very much faster 
than cold. Cold water, however, if given time enough, will 
remove impurities as completely as hot, the bleach required by 
the fibre being practically the same in both cases. If the fibre 
stands for any appreciable time in contact with the black liquor 
it appears to absorb coloring matter from the latter and be- 
comes very hard to bleach. This is particularly true where the 
mixture of fibre and black liquor becomes cold, twenty-four 
hours' contact under such conditions being enough to increase 
the bleach required from 9 to 14 to 15 per cent. On general 
principles the stock should be washed as soon as possible after 
discharging from the digester and access of air or cooling of the 
stock should be avoided as far as can be done conveniently. 
It is particularly important that the last traces of black liquor 

1 Beveridge: Paper, 25 (1919), 198. 



122 THE SODA PROCESS 

be removed before the stock reaches the bleaching system since 
even a very small amount renders bleaching quite difficult. 

The results obtained in any washing system depend on the 
judgment of the workmen and upon the care which they use. 
Frequent tests are necessary and the accuracy of the hydrom- 
eter and the temperature at which it is used should be care- 
fully looked to. A device which shows the progress of the 
washing by the color of the liquor can be installed at little 
expense by passing a small stream of the liquor continuously 
through a glass U-tube beside which is a gauge glass of the 
same diameter and color. The gauge is filled with black liquor 
of the minimum strength which it is desired to collect as strong 
or weak liquor, as the case may be, and when the color of the 
washings is the same as the standard the collection of washings 
of that grade is discontinued. 

After washing the treatment of the pulp is largely mechanical 
until it reaches the bleaching system. It is sluiced out of the 
wash pits by a heavy stream of water and run through screens 
to remove shives, uncooked pieces, or knots. It goes next, 
while in a highly diluted condition, over sand settlers which 
are long, shallow troughs with ' crossbars at intervals in the 
bottom, and in which sand, dirt, cinders, shives and other 
impurities settle out. From the sand settlers it goes to a series 
of extractors which remove a large part of the water and de- 
liver the pulp at a proper concentration for bleaching. During 
these processes the amount of water present per pound of bone 
dry fibre has been found to be about as follows : 

Lbs. 

In wash pits 3.5 

At knotters 87. 7 

At centrifugal screens and sand settlers 123-135 

Entering bleaching system 24. 5-27 

Leaks and mechanical losses of fibre should be carefully 
looked for throughout this process. With extractors of a type 
similar to the washers used on beating engines such losses 
should not amount to more than 1 to 1.5 per cent of the total 



^ 



BLACK LIQUOR 1 23 

fibre and the material lost will be found to consist largely of 
short fibres or broken fragments. 

The pulp produced by the soda process from poplar will 
bleach to a good white color with 8 to 12 per cent of bleach, 
while that from coniferous woods requires a considerably greater 
amount. In some cases it is not possible to reach a high white 
color without a treatment so drastic as to seriously weaken the 
cellulose itself. For this reason much of the soda pulp from 
coniferous woods is used in grades of paper which do not require 
a very white fibre. 

Black Liquor. It is claimed by Griffin 1 that the liquor in 
the digester at the end of the cook is light rose in color but 
that it immediately darkens on exposure to air. However this 
may be, the mass by the time it reaches the wash pits is a rich 
dark brown in color. This is due to the liquor and not to the 
fibre itself which when washed is of a light grayish brown 
shade. 

The black liquor removed from the fibre during the washing 
contains nearly all the alkali originally employed, together with 
over half the weight of the wood used. Griffin 2 gives the 
following analytical data for black liquor derived from a soda 
cook of poplar wood, all figures being based on the weight of 
total solids dried at ioo° C. 

Per cent 

Silica (SiCk) 0.11 

Oxides of iron and alumina (Fe 2 03 and AI2O3) o. 02 

Lime (CaO) o. 05 

Potash (K 2 0) o. 69 

Soda (Na20) 25. 69 

Carbon dioxide (CO2) 3 . 43 

Acetic acid 9. 89 

Organic matter extracted by naphtha boiling below 6o° C 1. 56 

Organic matter extracted by ether 7. 14 

Organic matter extracted by absolute alcohol 28. 26 

Organic matter extracted by water 17. 02 

Total alkali by titration of incinerated residue 44. 25 

1 J. Am. Chem. Soc, 1902, 24, 235-238. 

2 Ibid. 



124 



THE SODA PROCESS 



Other analyses of black liquor from poplar showed the presence 
of total alkali equivalent to 65.5 grams per liter of sodium 
carbonate. Of this total alkali 

25. 8 per cent was combined as acetate 
8. o per cent was combined as carbonate 

13 . 3 per cent was combined as hydroxide 

13 . 5 per cent was combined with insoluble organic acids 

39.4 per cent was combined with soluble organic acids. 

The proportion of caustic soda here present is much less 
than that necessary according to Klason 1 who states that 40 
per cent of the total alkali must remain unused in the black 
liquor and that even if the wood is present in great excess at 
least 25 per cent of the original alkali will be found unconsumed. 
Even the difference between poplar and spruce seems hardly 
great enough to account for such differences as these. More- 
over it has been proved that if less than 9 per cent of caustic 
soda is employed the wood uses it up completely, none being 
present in the black liquor. Even when 18 per cent on the 
weight of the wood is added fully 90 per cent of it is consumed 
and that remaining in the liquor is reduced to a strength of only 
about 1.4 grams per liter. Even under actual working condi- 
tions the proportion of caustic remaining unused is much less 
than that claimed by Klason, as the following analyses of black 
liquors from various woods will show: 



Kind of wood 


Black liquor 


Caustic remaining. 

Per cent on bone 

dry wood 


Grams per liter 
NaOH 


Per cent causticity 


White maple 

White birch 


I3-I-I4-3 

8.7-21.5 
20.2-22 .1 
10. 6-1 7. 6 

6. 4-18. 1 


21 .1-21 .4 
12.2-28.8 
33-3-35-6 
18. 5-21. 3 

I5-3-29-I 


5-0- 5.1 
2.9- 7.7 
9.8-IO.4 
4.6- 4.8 
3-5- 8.0 


Black gum 


Beech 


Poplar 





According to Griffin and Little 2 sodium formate, oxalate and 
acetate together with dark colored products similar to ulmic 

1 Christiansen: Natronzellstoff, p. 51. 

2 Griffin and Little: Chemistry of Paper Making, p. 164 (1894). 



BLACK LIQUOR I2 5 

acid have been recognized in the black liquor. Higgins l pat- 
ented in 1 89 1 a method for preparing acetates from black liquor 
by charring at not over 350 degs., but the process has never 
been practically adopted. 

Among other processes for treating black liquor, Rinman 2 
proposes to precipitate the humus substances with carbonic 
acid in the presence of salt and after drying the precipitate 
distilling it destructively to obtain acetone, alcohol, etc. Tests 
by the author on liquor from poplar wood show that only 9.2 
per cent of the total organic matter present can be precipitated 
by, carbonic acid and that after very slight washing this pre- 
cipitate is again readily dissolved by hot water. Veitch and 
Merrill 3 working with a black liquor from Southern pine which 
contained n.i per cent of organic matter in solution found that 
4.9 per cent was precipitated by carbon dioxide and a further 
1.2 per cent by acetic acid. Evidently the kind of wood used 
very greatly influences the amount of precipitate obtainable by 
means of carbon dioxide. 

The problem of the commercial utilization of black liquor is 
a very attractive one and many attempts have been made to 
obtain from it useful by-products. The humic matter precipi- 
tated from it by acids can be used as a sizing agent for paper 
but the pinkish color which it imparts limits its use to colored 
papers. It has been proposed to make a stain for wood from 
this organic matter and it can also be utilized in the manu- 
facture of brown sulphur dyes or nitrated to form brown to 
yellow dyes. None of these uses would make much of an im- 
pression on the vast quantities produced annually and in all of 
them the recovery value of the soda would be lost in the process 
of precipitating the organic matter. A more rational plan 
would be the destructive distillation of the black liquor in such 
a way that the volatile oils and other materials could be col- 
lected while the residual matter would still contain all the soda 

1 Higgins: Eng. Pat. 13,409, 1891. 

2 Rinman: Soda Recovery; Papier Ztg., 191 1, 3489. 

3 U. S. Dept. of Agriculture, Bureau of Chem., Bull. No. 159 (1913). 



126 THE SODA PROCESS 

in available form for reuse. The products obtained from such 
a treatment are non-condensable gases, methyl alcohol, acetone, 
aldehydes, amines, phenolic oils, tar and the retort residue con- 
taining the alkali and carbon. Adding lime to the charge be- 
fore distilling increases the amount of acetone in the distillate 
while if no alkali is added the methyl alcohol is present in much 
the greater amount. 

Recovery of Soda. The regeneration of the soda was not 
attempted in the early days of the process but it was soon 
rendered necessary by the difficulty in disposing of large quan- 
tities of the waste' liquors and by the expense of repeatedly 
replacing the entire amount of alkali. The character of the 
waste is such as to render recovery especially easy from a chemi- 
cal standpoint, for about one-half of the fuel value of the wood 
is present in the liquor and it is in such form that its combus- 
tion furnishes a large part of the heat necessary to evaporate 
the liquors to the point where they may be ignited. After 
burning the soda remains as carbonate in the black ash. While 
the process of recovery is comparatively simple, the necessary 
equipment is the most expensive, part of the soda mill and its 
efficiency has an important bearing on the cost of production. 

According to Griffin and Little 1 the mixture of waste liquor 
and washings to be treated usually tests from 6° to 9 Be. at 
160 F. and in order to maintain continuous combustion it is 
necessary to concentrate to at least 30 Be. at 130 F., and still 
better to bring it up to 40 Be., or higher. Of the very large 
amount of water which it is necessary to evaporate during this 
process, part comes from the moisture in the chips and from 
the liquor originally added, part from the water used in washing 
and part from the steam condensed during the cooking. This 
latter item is greater during cold weather and would be some- 
what less for stationary digesters because of the better heat 
insulation in this type of apparatus. 

Recent examinations of black liquor from poplar wood pro- 
duced the following data. 

1 Griffin and Little: Chemistry of Paper Making, p. 164 (1894). 



RECOVERY OF SODA 



127 









Boiling points in degrees C. at * 




Degrees Be. at 


Grams dry 
matter per 100 










room tempera- 












ture 


grams liquor 


41 inches 


20 inches 


inches 


10 inches 


25 inches 






pressure 


pressure 


pressure 


vacuum 


vacuum 


7 


7.8 


124. s 


H4-3 


IOI 


9°-5 


58.5 


16 


18.5 












22 


27 .1 


128.O 


H7-5 


• 104 


93 -o 


62.O 


27 


36.6 












32 


46.8 












37 


57-6 


135-5 


124.7 


112 


100.9 


69.O 



* Records for pressure and vacuum are in inches of mercury. 

The proportions of organic and inorganic constituents in black 
liquor are indicated in the following analyses which were made 
on an average sample of the liquor first draining away from the 
stock; this liquor tested i2f° Be. at 70 F. 



Total solids 

Water 

Caustic soda 

Total alkali as Na 2 

Organic matter precipitated by H2SO4 



Grams per 


Per cent by 


liter 


weight 


180.2 


16.4 


917-3 


83.6 


19-5 


1.8 


49-9 


4-5 


27-3 


2.6 



Per cent on 
total 
solids 



10.8 
27.7 
15-2 



In practice the evaporation of black liquor is performed either 
in open pans or vacuum apparatus. The Porion evaporator, 
which is representative of the first class, consists of a brick 
chamber, the lower part of which forms a shallow reservoir, 
and through which pass two cross shafts driven from the out- 
side. These two shafts carry a series of paddles which when 
revolved at high speed throw the liquor into the upper part of 
the chamber in the form of a fine spray. At one end of this 
chamber is the calcining furnace where the final concentration 
and incineration of the black liquor take place. The burning 
is assisted by a coal fire at one end of this furnace and all prod- 
ucts of combustion pass through the evaporating chamber on 
their way to the chimney, thus heating and evaporating the 
liquor and being themselves cooled in the process to 85 C. or 



128 THE SODA PROCESS 

even lower. When the liquor in the chamber has reached a 
density of 26 to 29 Be. it is removed to a storage tank over 
the calcining furnace from which it is gradually fed into the 
latter. This evaporator costs comparatively little for erection 
and operation and it is claimed will yield three-quarters of a 
ton of ash per ton of coal. 

Enderlein's evaporator is similar in principle but the arms 
which produce the spray are replaced with wrought iron discs 
about six inches apart which revolve partly in the liquor and 
thus carry a thin film of liquid up into the gases which are 
obliged to pass between the discs before reaching the chimney. 
According to Beveridge : the fuel economy of this apparatus is 
nearly as good as that of multiple effect evaporators. 

The vacuum or multiple effect evaporators depend on the 
fact that the boiling point of water, or other liquid, is lowered 
by reducing the pressure under which it boils. The boiling 
temperatures for black liquor already given in the accompanying 
table illustrate this, and these will be found to follow very 
closely .the boiling points of water under similar conditions. 
Apparatus working on this principle is so constructed that the 
steam from the liquid evaporated in the first section, or " effect," 
is used to boil that in the second effect, this being kept under 
enough lower pressure so that active ebullition takes place. The 
steam from the second effect in turn boils the liquor in the third 
effect and so on through the system which may consist of three 
to five effects. The only necessity for heat from outside sources 
is therefore in the first effect in which the liquor is raised from 
the entering temperature to the temperature of ebullition at the 
pressure in this effect. The pressure in the first effect varies 
greatly in different mills and with different types of apparatus. 

One of the evaporators most frequently used in soda pulp 
mills is the Yaryan in which the liquor passes back and forth 
through the tubes and finally is discharged against baffle plates 
in a separating chamber. The tubes are 3 ins. in diameter 

1 Beveridge: Paper Makers' Pocket Book, p. 106. 



RECOVERY OF SODA 



129 





Fig. 17. Y Aryan Evaporator 
Courtesy of Mr. Chas. Ordway 



13° 



THE SODA PROCESS 



and 12 ft. long and as five tubes form a unit the liquor travels 
60 ft. before it is discharged. From this chamber the steam 
passes into the shell of the next effect while the liquor goes to 
the tubes. The vacuum is maintained by means of a con- 
denser and pump and the strong black liquor is removed from 







Fig. 18. Y Aryan Evaporator Feed end of one Effect .' 
Courtesy of Mr. Chas. Ordway 

• the last effect by another pump which usually discharges it 
into tanks over the furnaces. The efficiency of the Yaryan is 
said to be due in part to the rapid motion of the liquor through 
the tubes and the more rapid absorption of heat which results. 
The time required for liquor to pass through all the effects is 
but a few minutes, and as only a small amount of liquor is 
present at any one time the evaporator can be started and 
stopped very quickly. 



EVAPORATORS 



131 



Several types of Yaryan evaporators are on the market. Fig. 
17 shows a horizontal evaporator in general view and a section 
of one effect, while Fig. 18 shows the feed pipes and the return 
bends of part of the coils. It is to be noted that uniform feed 
for all coils is insured by bringing the feed pipes all down to one 
level. 

In other types of multiple evaporators the positions of the 
steam and liquor are reversed, the steam being in the tubes 



Vapor Outlet 




Fig. 19. Zaremba Evaporator Vertical Cross Section of one Effect 
Courtesy of Zaremba Company 

while the liquor to be concentrated flows over them by gravity 
in a thin film. The Zaremba evaporator, a cross section of 
one effect of which is shown in Fig. 19, is of this type. This 
evaporator is giving good service on black liquor and in one 
installation a four-effect evaporator with bodies 14 ft. in diam- 
eter is handling 350,000 gals, daily. 



132 THE SODA PROCESS 

Numerous tests on both types of evaporators have proved 
that an evaporation of 3 to 3! lbs. of water from and at 212 F. 
can be maintained under ordinary working conditions, while 
if the heat necessary to bring the liquor to the boiling point is 
considered the evaporation would be somewhat less, say 2.6 to 
2.9 lbs. of water per pound of steam. Assuming an evapora- 
tion of 8| lbs. of water per pound of coal under the boilers the 
patentees of the Yaryan evaporator claim that a double effect 
will evaporate 16 lbs., a triple effect 23^ lbs. and a quadruple 
effect 30! lbs. of water per pound of coal. Tests under ordi- 
nary running conditions have shown an evaporation, for a 
three-effect Yaryan, of 18 to 20 lbs. of water per pound of coal 
on the above assumption. 

After evaporation the liquor goes to a storage tank and thence 
to the incinerating furnace. This furnace consists of a revolv 
ing, cylindrical shell lined in such a way that the interior is 
somewhat conical with the large end toward the fire box. Mod- 
ern furnaces are quite generally about 20 ft. long and 9 ft. out- 
side diameter, but some are built as much as 30 ft. long. The 
lining is of ordinary hard-burned red brick and is about 15 ins. 
thick at one end and 9 at the other. The placing of pieces of 
cast iron at intervals helps to resist wear; the links of old chain 
grates placed edgewise have proved very good for this purpose. 
The furnace is mounted on wheels and fitted with a gear by 
which it is caused to turn at a speed of one to three revolutions 
per minute according to the condition of the liquor supply. 

At the discharge end of the furnace there is a fire box, 
mounted on wheels which rest upon rails so that the whole can 
be drawn back out of the way when the furnace proper needs 
repairs. This fire box is arranged to burn coal, wood waste, gas 
or oil according to local conditions. It is usually impossible to 
get a very accurate estimate of the fuel burned per ton of ash 
because the use of waste material is so general. In one mill 
where both wood and coal were burned the amount of the latter 
was only 120 lbs. per ton of ash produced. During a test on 
a 20-ft. furnace burning all coal with a moisture content of 2.33 



LEACHERS 1 33 

per cent, and running liquor at 38 Be., the coal burned per 
ton of ash produced was 117 lbs., while under similar conditions 
325 lbs. of shavings with a moisture content of 39 per cent were 
required. 

Fig. 20 shows diagrammatically the arrangement of a modern 
recovery plant with its rotary furnace, fire box and boiler set- 
ting for the recovery of waste heat from the incinerator. Such 
a boiler will produce a very considerable part of the steam neces- 
sary for the evaporation of the black liquor. In one plant the 
boiler over a furnace burning 21 tons of ash per day developed 
150 to 160 horse power when it was in good condition. 

The strong black liquor which enters the back end of the 
furnace is not yet concentrated enough to support its own 
combustion. As it works forward in the furnace it loses water 
and finally takes fire, the organic compounds are destroyed 
and it is finally discharged in a glowing condition containing 
practically only carbon and sodium carbonate. If it is well 
burned there is at most a slight blue flame to the discharged 
ash, but if the furnace is pushed a little too hard the ash may be 
under-burned in which case it may show considerable yellow 
flame even after it is dumped into the leaching tanks. Under 
ordinary conditions a 20-ft. furnace operated by experienced 
men will produce 30 to t,^ tons of ash in twenty-four hours 
and under exceptionally favorable conditions the product may 
go as high as 42 to 43 tons. The lining of such a furnace will 
not last much over six months and if it is pushed harder than it 
should be it will need repairs rather sooner. 

The recovered ash in the soda process will contain 65 to 80 
per cent of sodium carbonate according to the care with which 
it has been burned. There are small amounts of iron, alumina, 
lime, sulphur and silica derived from various sources and about 
18 to 22 per cent of carbon. 

From the furnaces the ash goes to some form of leaching 
device, either open tanks or closed tanks to which pressure can 
be applied. In the open tanks it is first flooded with weak 
liquor from below in order to avoid causing explosions when 



134 



THE SODA PROCESS 




pq 



LOSSES 135 

water comes in contact with the glowing ash. The washing 
is carried out systematically in order to produce a leach liquor 
of good strength and at the same time lose as little soda as 
possible. The closed tank system saves floor space and time 
in leaching but much care is necessary in order to avoid explo- 
sions. There seems to be little to choose between the two 
systems so far as operating efficiency is concerned. 

Black Ash Waste. This material, which remains in the leach- 
ing tanks at the end of the washing, consists of light porous car- 
bon contaminated with small amounts of impurities. Because 
of its physical condition it is very difficult to remove the water 
it contains. When drained as much as possible in the leach 
tanks it still contains 80 to 85 per cent of water, even in the top 
layers which are driest. The use of a centrifugal machine will 
not reduce this moisture below 65 to 68 per cent and beyond 
this point it can be dried only by the application of heat. 

The following analysis gives an idea of the composition of this 
waste. The sample had been thoroughly dried and then exposed 
to the air. 

Per cent 

Moisture, H 2 6. 06 

Sodium carbonate, Na 2 C03 2.51 

Calcium carbonate, CaCC>3 1. 17 

Sodium sulphide, Na 2 S o. 37 

Magnesia, MgO o. 34 

Iron and alumina, Fe 2 C>3 and Al 2 03 o. 26 

Silica, Si0 2 o. 17 

Calcium sulphate, CaSCu o. 07 

Carbon by difference, C 89. 05 

No use for this material, which will even begin to take care 
of the amount made, has ever been developed. The most 
promising field seems to be as a fuel, since the heating value of 
the dried waste is 14,000 to 14,500 B.T.U. 

Losses. The chief loss to which attention should be paid is 
that of soda. This occurs at numerous points, all of which should 
be subjected to careful scrutiny. 

The loss in the lime mud should be checked by routine analy- 
ses. These will indicate whether the process is being run care- 



136 THE SODA PROCESS 

fully and may prove that a different lime can be used which 
will permit better settling and cleaner washing. The loss in 
the waste lime sludge will be about 2.0 per cent of its dry weight 
under average conditions. 

The loss in washing out the black liquor from the fibre may 
be studied by analyses and volume measurements of the final 
washings. Such studies indicate that under normal conditions 
this loss will amount to 1 to 1.5 per cent of the total soda used 
in the digesters. There is also a loss due to the presence of a 
small amount of soda in the washed fibre; this has been found 
to be about 1.5 per cent of the soda used. Under abnormal 
conditions, as when the recovery plant cannot keep up with 
the wash pits, there is likely to be a much greater loss in the 
final wash water. 

The losses in burning the black ash are hard to determine 
because the process is a continuous one and reliable measure- 
ments of the materials going to and coming from the furnaces 
are seldom made. Moreover the loss is chiefly in material 
carried up the stack mechanically or because of a slight vola- 
tilization of soda. Spence * has studied the loss up the flues 
and gives the soda lost per twenty-four hours as follows for 
different sizes of incinerators. 

Lbs. 

14-foot rotaries 450-1000 

16-foot rotaries 650-1300 

30-foot rotaries 2500-4000 

In the leaching of the black ash there is a loss of soda which 
may run from a few tenths of a per cent up to four or five per cent 
for unsatisfactory conditions. While it would seem an easy 
matter to determine this loss it has proved to be a very difficult 
proposition because the nature of the material and the way it 
is handled make it almost impossible to obtain a fair sample. 

Tests and Analyses for the Soda Process. The analytical 
work necessary for the control of the soda process is of a com- 
paratively simple nature. The materials which should be tested 
1 Spence: Paper, 1919, 619. 



TESTS AND ANALYSES 137 

either regularly or at intervals are the cooking liquor and black 
liquor, soda ash, lime, lime mud, black ash and black ash waste. 
The cooking liquor contains caustic soda as the essential in- 
gredient, but it also contains soda ash and in some cases salt, 
which renders its valuation by a simple hydrometer test some- 
what misleading. The actual grams per liter of caustic soda 
should be determined by titrating 10 c.c. with normal acid 
using first phenolphthalein and finally methyl orange as indi- 
cator. The methyl orange shows the total alkali while the 
phenolphthalein shows all the caustic soda and half the car- 
bonate. Twice the difference between the two, subtracted 
from the methyl orange reading, gives the acid to neutralize 
the caustic soda and this multiplied by 4 gives the grams per 
liter of NaOH. The causticity of the cooking liquor should 
also be recorded; this is obtained by dividing the cubic centi- 
meters of acid required for the caustic soda by the volume 
necessary for the total alkali. Probably most practical mill 
men would say that the Baume test is the only one necessary 
but for the reasons given above this test alone may lead to 
entirely incorrect conclusions. 

Soda ash is ordinarily one of the purest of commercial chemi- 
cals yet it is desirable to test it occasionally when received and 
if it is stored in bulk it is sometimes necessary to determine 
the amount of moisture which it has taken up. For moisture 
a representative sample of 1 to 2 grams is accurately weighed 
into a platinum crucible and dried for three-quarters of an hour 
over a gas flame which is so adjusted that the bottom of the 
crucible just shows a faint redness when shielded from strong- 
light. After cooling in a desiccator it is quickly reweighed, the 
loss being calculated as percentage of moisture. For the de- 
termination of alkali present the dried sample is dissolved in 
water and titrated with normal acid using methyl orange as 
indicator. The percentage of sodium carbonate in the original 
sample is calculated by the following formula 

C. C. acid X 0-053 

Weight of sample before drying 



138 THE SODA PROCESS 

The lime used in causticizing should be regularly tested in 
order to see that its quality is kept up to a reasonable standard. 
A chemical analysis will not necessarily show what results it 
will give in practice but a simple causticizing test made under 
conditions similar to those of actual work will give very valu- 
able information. From each car of lime received as fair a 
sample as possible should be taken by going all over the car 
and taking portions from the top, middle and bottom of the 
load. This should be selected to represent both the fine and 
the coarse material and as soon as the entire sample is taken it 
should be crushed and quartered down as rapidly as possible 
to avoid the absorption of moisture. From this final sample a 
weighed amount is taken and boiled for exactly one hour with 
water and a weighed amount of dry soda ash which is in excess 
of the amount the lime can causticize. The amount of water 
used is so taken that the final solution at the end of the test 
is about the strength of that used in practice. After the boiling 
is completed the sludge is allowed to settle and the clear liquor 
is titrated with both phenolphthalein and methyl orange as in 
the case of cooking liquor. Knowing the causticity from this 
titration and the weight of soda ash taken the amount of lime 
required to causticize 100 lbs. of dry soda ash may be calculated 
by this formula: 

Weight of lime used X 100 
Per cent causticity X weight of soda ash used 

The settling quality of the lime may be ascertained in this 
same test by taking a sample of the rapidly boiling mixture 
just at the end of the test and, without giving it time to settle, 
filling a 100 c.c. graduate just to the upper mark. By noting 
the cubic centimeters of clear liquor at fixed time intervals the 
relative settling qualities of the various limes can be compared. 

The lime mud which settles in the causticizing and washing 
tanks is generally a waste product and in order to see that 
too much caustic socla is not thrown away it should be tested 
at intervals for the amount of alkali present. A representative 
sample of the dried mud is weighed out, placed in a small por- 



TESTS AND ANALYSES 1 39 

celain dish and moistened with strong ammonium carbonate 
solution. It is next evaporated to dryness, heated over a low 
flame until no odor of ammonia can be noticed, and finally 
leached out repeatedly with boiling distilled water until all the 
soluble alkali is removed. The combined leachings are then 
titrated with standard acid, using methyl orange as indicator, 
and the results calculated to precentage of alkali based on the 
dry lime mud. 

In the case of black liquor it is at times desirable to know 
the strength both in total alkali and in free caustic soda. For 
total alkali evaporate a measured volume to dryness in a plati- 
num dish and ignite over a flame till the organic matter is com- 
pletely carbonized. Cool, extract several times with hot water 
and pour the extracts through a small platinum cone. Put the 
cone in the dish together with the residual wet carbon, cover 
with a filter paper which just fits inside the dish and quickly 
ignite over a gas flame. The filter paper prevents loss by 
spattering and enables the carbon to be burned off without 
waiting for it to be dried first. Again cool and extract with 
hot water, add the extract to the first and titrate with acid in 
the presence of methyl orange. Calculate the results to grams 
of sodium carbonate per liter or pounds per gallon. 

For the determination of free caustic soda in black liquor 
add 25 c.c. of the latter to 400 c.c. of water and 15 c.c. of barium 
chloride solution (400 grams per liter) in a beaker. Titrate 
directly with standard acid using a dilute solution of phenol- 
phthalein on a spot plate as an indicator. The acid should be 
added quite slowly and the end point may be considered as 
that point at which no pink color develops within two minutes 
after mixing one or two drops of the liquid with the indicator. 
Owing to the presence of soluble coloring matter and to the 
precipitate thrown down by the barium chloride the end point 
is not very sharp but with a little practice it is fairly easy to 
get concordant results. A sharper end point is obtained by 
filtering off or settling out the barium precipitate and using 
only the clear liquor, but this introduces a distinct error due 



140 THE SODA PROCESS 

to the loss of the caustic soda occluded by the precipitate. In 
the method outlined above this is kept within the sphere of 
action of the acid and more accurate results are obtained. 

Analyses of black ash and black ash waste are usually con- 
fined to simple determinations of the amount of soluble alkali 
present. In the case of black ash this may be leached out with 
hot water and titrated as usual in the presence of methyl orange. 
With black ash waste the volume of carbon is relatively so 
large that it is well to burn off most of it in a platinum dish 
before attempting to leach out the soda. 



CHAPTER V 
THE SULPHATE PROCESS 

The sulphate process is similar to- the soda process in that the 
cooking liquor is alkaline, but it differs from it by replacing the 
alkali lost with sodium sulphate instead of soda ash. In, rare 
cases both are used but the sulphate is always in the greater 
amount and it is from the use of this material that the process 
gets its name. Actually it is a misnomer, and it would be better 
to call it the sulphide process because of the important part 
played by sodium sulphide in the cooking liquor. This sulphide 
is derived from the sulphate by reduction in the recovery of the 
alkali and it is this feature which introduces the greatest deviation 
from the soda process. 

There is more or less confusion in the use of the terms " sul- 
phate" and "kraft" as applied to the process and products. 
Sulphate may be considered as a general term applying to any 
cooking process in which the loss of alkali is made up by adding 
sodium sulphate, while kraft is that subdivision of the sulphate 
process in which the pulp is intentionally undercooked in order 
to produce very strong stock. The products of the sulphate 
process vary according to the cooking conditions from the dark 
brown, unbleachable kraft fibre to a soft, easy bleaching stock. 
The latter may be used in making white papers where it gives 
a soft, pliable sheet in comparison with the harder and more 
rattly paper from sulphite. The principal use of the sulphate 
process however is in the preparation of kraft stock. 

The sulphate process has two chief advantages over the sul- 
phite process: the chemicals used can be recovered and the 
wood used may be of a highly resinous nature. It is this second 
fact which gives the process its widest application. As compared 

141 



142 THE SULPHATE PROCESS 

with the soda process it gives somewhat higher yields and employs 
a cheaper source of alkali. Its one disadvantage lies in the 
extremely disagreeable odors due to the organic sulphur com- 
pounds formed during cooking and recovery. This has been 
found serious enough to limit its use to sparsely inhabited local- 
ities. 

As the process is an alkaline one there is no appreciable action 
upon the digester plates and it is not necessary to use any lining. 
The equipment used is very similar to that for the soda process 
though the digesters are, as a rule, smaller, yielding from two to 
three tons of pulp per charge. There is a tendency in Europe 
towards the use of digesters which rotate on their short axes. 
The sizes of these are variously reported as 1 8 to 45 cubic meters 
capacity (635 to 1590 cu. ft.). The digesters should always be 
welded and not riveted, as the latter are bound to develop leaks 
from the continual expansion and contraction to which they are 
subjected. 

The cooking process employed depends on whether kraft fibre 
or easy bleaching stock is to be produced. For kraft fibre in 
which a dark color is desired a portion of the cooking liquor is 
made up of black liquor containing practically no caustic soda. 
The proportion of this black liquor, as might be expected, varies 
considerably, some mills using as little as 27 per cent while in 
others it amounts to nearly 60 per cent of the total liquor. The 
volume of liquor used is about 45 to 50 per cent of the capacity 
of the digester and it tests 8° to 12 Be. at 6o° C. if indirect heat- 
ing is employed or 18 to 23 Be. when steam is blown into the 
charge. Beveridge 1 states that the total volume of liquor 
should not be less than 150 cu. ft. per 2000 lbs. of air-dried 
pulp produced, or per 1.60 cords of wood. The relative volumes 
of white and black liquor would then depend on the strength of 
the former as delivered by the causticizing system, any excess 
over the volume of white liquor necessary to give the required 
amount of alkali being made up by black liquor. The alkali 
required in making kraft fibre is said to be 640 lbs. per ton of pulp. 

1 Beveridge: Paper, 1918, 22, 21. 



RELATIVE VALUE OF ALKALIS 



J 43 



The cooking time is from i| to 6 hours and the steam pressure 
employed varies from no lbs. to 135 lbs., the highest pressure 
being held for only i| to 2 hours. In practice it is seldom neces- 
sary to cook at more than no lbs. pressure. For easy bleaching 
fibre no black liquor is used and if the cooking liquor has to be 
diluted water only is employed. The other cooking conditions 
are about the same as they are for kraft fibre. 

A modification of the usual cooking process is that proposed 
by Ungerer 1 in which the cooking liquor is passed through a 
series of digesters until exhausted. The original installations 
were of small digesters and the process has never been very 
extensively used. The chief trouble seems to have been in keep- 
ing the liquor heaters in repair, while the advantages claimed 
were more uniform, stronger and easier bleaching fibre. The fol- 
lowing figures 2 show the strength of the various constituents in 
a definite quantity of the liquor as it passes the digesters in series. 



Digester 


Total soda as 
Na 2 


Soda combined 

with organic 

matter 


Soda as NaOH 


Soda as Na2C0 3 


2 

3 

4 
5 
6 

7 


874 
729 

657 
611 
605 
598 


251 
543 
579 
552 
558 
582 


298 
31 

22 

9 
3 



325 
155 
56 
5° 
44 
16 



From experiments in the Forest Products Laboratory 3 it has 
been proved that increasing the amount of either the caustic 
soda or the sodium sulphide decreases the yield and that the 
former has about twice as much influence as the latter. The 
carbonate and sulphate of sodium are apparently without effect 
on the wood. This has been confirmed by observations under 
•actual working conditions and Beveridge 4 expresses the opinion 

1 Ungerer: Papier Ztg., 22 (94), 3360. 

2 Knosel: Papier Ztg., 22 (97), 3470. 

3 Wells: Paper, Sept. 24, 1913, p. 15. 

4 Beveridge: Paper, 19 18, 22, 21. 



144 



THE SULPHATE PROCESS 



that the caustic soda unites with the organic matter first and 
when exhausted, or nearly so, the sulphide comes into play. 

The composition of sulphate cooking liquor, according to 
several different authorities, is given below in tabular form, the 
quantities of the various substances being expressed as grams per 
liter. 



Authority 


Na 2 C0 3 


NaOH 


Na 2 S 


Na 2 S0 3 


Na 2 S0 4 


Deg. Be 


M. Muller * 

Schacht * 

Schacht * 

Heuser f 

Klein J 


24.00 
36.00 
45-05 
7.48 
15.00 
10.00 


45.00 
80.60 
77.80 
61.80 
62 .00 
55- 00 


13.00 
I3-SO 
11.25 
25.12 
22 .00 
30.00 


2.00 

7-25 
8.19 
3-78 
3.00 
3-00 


14.00 

15.10 

12.18 

4-52 

5.00 


i 7 '.8 
18.5 







* Kirchner: Das Papier, p. 109. 

t Heuser: Papier Ztg., 1910, p. 1511. 

t Klein: Papier-Fabr., 1914, p. 628. 

From the investigations of E. Heuser 1 on beechwood it appears 
that comparatively little sodium sulphide is used up during the 
process. The following table shows the strength of the cooking 
liquor used in three of his cooks and the percentages of the indi- 
vidual constituents consumed. 



Na2S added in grams per liter 

NaOH added in grams per liter. . . . 
Na2C03 added in grams per liter. . . 
Percentage consumption of Na 2 S. . . 
Percentage consumption of NaOH . 
Percentage consumption of Na2COs 



I 


2 


19-50 


24.70 


27-75 


48.55 


18.00 


22 .00 


7-95 


15.60 


69.80 


51.20 


39.00 


6.40 



21 .40 
28.20 

9-9° 
7 .00 
63-80 
2.80* 



* Percentage Increase 

In all three cooks the Na 2 S0 4 present increased very slightly 
during the cook. 

The materials necessary to produce one ton (2000 lbs.) of 
sulphate pulp vary quite widely in different mills; the following 
seem to be the limiting values: 

1 Heuser: Wochbl. Papier-Fabr., 1913, p. 2209. 



YIELD OF FIBRE 145 

Wood 177-247 cu. ft. 

Coal S50-770 lbs. 

Sodium sulphate 320-395 lbs. 

Lime 530-660 lbs. 

The washing, screening and bleaching of sulphate pulp differ 
in no essential detail from the treatment accorded soda pulp. It 
is most general to use diffusers to wash the black liquor from sul- 
phate pulp but there is no reason why open pans could not be 
used and there is considerable difference of opinion as to the rela- 
tive advantages of the two methods. It is claimed that the size 
of the plant influences the choice, diffusers being satisfactory for 
small installations and open pans for large ones. As it is desirable 
to have five or six diffusers to each digester the cost of installation 
is high in plants of large capacity. Moreover their life is com- 
paratively short, — about ten years, — due to the pitting and eat- 
ing away of the steel. 

The yield of fibre by the sulphate process, as already stated, 
is greater than by the soda process. According to Kirchner 1 the 
yields for spruce (Fichte) and fir (Kiefer) are: 





Soda 


Sulphate 


Sulphite 


Spruce 


Per cent 
29.7-32.8 
28.0-29.3 


Per cent 
32.8-35.9 
29.3-32.0 


Per cent 

37-50 


Fir 







Experiments by the author gave the following yields per cord, 
assuming that there are 100 cu. ft. of solid wood per cord: 





Soda 


Sulphate 


Poplar (Populus sp ) 


Pounds 

1007 

699 

790 

786 


Pounds 
1 130 

773 
862 


White pine (Pinus strobus) 


Pitch pine (Pinus rieida) 


Spruce (Picea sp ) 


956 





1 Kirchner: Das Papier, IV, 358. 



146 



THE SULPHATE PROCESS 



In addition to the greater yield the sulphate fibre bleaches 
considerably easier than soda fibre from the same wood. 

The blow-off gases from sulphate cooks have been the subject 
of much investigation in Sweden and Germany. Bergstrom and 
Fagerlind 1 have found in them methyl mercaptan, dimethyl 
sulphide, dimethyl disulphide, methyl alcohol, ammonia, turpen- 
tine, rosin oil, hydrogen sulphide, ammonium sulphide, and 
acetone. The evil odors of the process are due in large part to the 
first two compounds of which the mercaptan is far the worse. 
According to Klason and Segerfeld 2 about 100 grams of mer- 
captan are produced per ton of wood treated in making easy 
bleaching pulp while ten times as much may be obtained in kraft 
cooks. Pine yields about twice as much as spruce. According 
to Falk 3 the condensed materials obtained per ton of cellulose 
from pine wood are as follows: 



In oily portion 



In aqueous 
portion 



Mercaptan 

Dimethyl sulphide . . 
Dimethyl disulphide. 

Turpentine 

Distillation residues . 

Methyl alcohol 

Ammonia 



Kgs. 
0.062 
0.927 
0.103 

8.487 
0.721 



Kgs. 
0.06 
0.17 
0.05 
0.92 



5 -oo 
0.18 



From work done at the Billingsfors mill the condensed steam 
from the digesters was found to yield the following quantities 
for every ton of finished pulp made. 

Lbs. 

Turpentine 17.6 (from fir) 

Turpentine 2.2 (from pine) 

Methyl alcohol 1 1 . o 

Methyl mercaptan 2. 2 

Methyl sulphide 6. 6 

Methyl bisulphide 0.2 

Ammonia 0.4 

1 Papier-Fabr., 1909, 7, 7, 27, 78, 104, 129. 

2 Papier-Fabr., 1911, 9, 1093-1099. 

3 Papier-Fabr., 1909, 7, 469-472. 



BLACK LIQUOR 147 

Bergstrom 1 states that in 191 2 five sulphate mills were recover- 
ing methyl alcohol. Pine and spruce yield about the same 
amount, 15 kgs. per 1,000 kgs. of cellulose, and of this 5 kgs. are 
collected in the condensed vapors while further amounts may be 
obtained from the vapors formed during evaporation of the black 
liquors. The cost of such recovery is slight and the process in no 
way interferes with regular operations of the mill. 

Klason 2 has carried out extended investigations of the sulphate 
process in the attempt to eliminate the odors. He found that the 
gases could be almost entirely freed from mercaptan by passing 
through solutions of various metallic salts but that the only 
metallic mercaptides which were completely odorless were those 
of the noble metals. Caustic soda will also absorb mercaptan 
but not methyl sulphide. The gases, separated from entrained 
liquid, can be rendered harmless by passing them under a furnace 
grate but explosions must be guarded against. Oxidizing agents, 
as bleach or permanganate, will destroy the odors but they also 
oxidize the alcohol and the quantity necessary is therefore exces- 
sive. 

The black liquor from the sulphate process has been inves- 
tigated repeatedly. According to Klason and Segerfeld 3 of the 
organic matter present 54.3 per cent is lignin; 2.5 per cent fatty 
and resin acids; 3.7 per cent formic acid; 5.2 per cent acetic acid 
and 30.3 per cent lactonic acids. Of the sulphur originally 
present as alkali sulphide 51.8 per cent was combined with 
lignin, 15 per cent expelled as volatile compounds, 16.8 per 
cent remained as alkali sulphide and 16.4 per cent was unac- 
counted for. 

The committee appointed by the Finnish Government 4 in 
1908 gives the following composition for a black liquor with a 
specific gravity of 1.140 from a Swedish mill. 

1 Papier-Fabr., 1912, 10, 677. 

2 Papier Ztg., 1908, 33, 3577. 

3 Papier-Fabr., 1911, 9, 1093-1099. 

4 Papier Ztg., 1910, 35, 2744. 



148 THE SULPHATE PROCESS 

Per cent 

Sodium carbonate (Na2COa) 2. 75 

Sodium hydroxide (NaOH) o. 45 

Sodium sulphide (Na 2 S) 1.76 

Sodium sulphate (Na 2 S04) 1.21 

Sodium sulphite (Na 2 S03) 0.16 

Sodium chloride (NaCl) o. 17 

Sodium thiosulphate (Na2S 2 03) o. 14 

Soda combined with organic acids 2. 25 

Organic acids n. 71 

Water, etc 79- 40 



100. 00 



An interesting proposal for handling the black liquor is that 
of Rinman. 1 He concentrates the liquor to about 90 grams per 
liter of Na 2 0, adds salt (NaCl) to a strength of about 40 grams 
per liter and precipitates the humus matters with carbon dioxide 
at a temperature of 75 C. The humus matters may be washed 
with water, provided no sodium sulphide is present, and may 
then be subjected to destructive distillation. The solution, freed 
from humus, may be treated by the ammonia-soda process for 
the recovery of the alkali as bicarbonate. The original plan, to 
recausticize and use it over again several times before sending it 
to the reclaiming system, has not proved practical because of 
the accumulation of substances not precipitated by carbon 
dioxide. 

As an alternative to this process Rinman suggested mixing the 
black liquor, after evaporation, with lime or caustic soda and 
distilling destructively in presence of steam at a temperature of 
400 C. This would result in the formation of fuel gases, acetone, 
alcohol, ketones, hydrocarbons, cresols, etc., and the residual 
carbon would contain the alkali which could be leached out and 
recovered. An experimental plant at the Stora Kopparsberg mill 
gave the following yields per ton of pulp made from pine or fir: 

Lbs. 

Pure acetone 39. 6 

Motor spirit 59-4 

Motor oil 121. o 

1 Rinman: Papier-Fabr., 191 2, 10, 39 and 101. 



SODA RECOVERY 



149 



These proposed methods are rather complicated and have not 
been generally adopted, much the greater proportion of the 
alkali being recovered by the usual methods. These consist of 
evaporation by any of the well known multiple effect evaporators, 
by disc evaporators or combinations of the two. When both are 
used the multiple effect takes the weak liquor and brings it up to 
about 2o°'Be., then it passes to the disc evaporator which concen- 
trates it to about 35 Be. According to Beveridge x in a well 
equipped mill the water which the recovery process must handle 
per 2000 lbs. of pulp is derived from the following sources: 





Cubic feet 


Per cent 


Water from chips 


47.6 
42.48 

67-33 
3I-50 


25 .1 


Water from steam 


22 .5 


Water from white liquor 


35 .6 


Water used for washing 


16.6 








188.91 





After concentration to about 35 Be. the liquor, which contains 
approximately equal weights of water and total solids, goes to the 
rotary furnaces. These are similar to the furnaces used in soda 
mills but are sometimes as long as 30 to 35 ft. As the liquor 
works forward in the furnace it becomes more concentrated and 
finally burns to a moist, black mass still containing a considerable 
amount of organic matter and water. In this form it is dis- 
charged in close proximity to the smelting furnace into which it is 
to be fed. During the passage of the liquor through the furnace 
rings are sometimes formed which hold it back while allowing the 
soda near the discharge end to become melted by the heat from 
the smelting furnace. When the ring finally breaks and the 
liquor runs into the melted mass explosions are very apt to occur. 

After being discharged from the rotary furnace the mass is 
mixed with enough sodium sulphate to replace the alkali lost and 
is then shoveled by hand into the smelting furnace. This is a 
chamber about four feet square by seven feet high, lined with 
soapstone to which the molten alkali does not adhere, and so 

1 Beveridge: Paper, 1918, 22, 349. 



IS© 



THE SULPHATE PROCESS 



constructed that oxidation of the sodium sulphide is reduced to a 
minimum. Combustion in the smelting chamber is provided 
for by an air blast entering through tubes which are water-cooled 
or sometimes made of platinum. The condition of the entering 
ash and the blast must be most carefully regulated to insure 
proper results. Moreover the furnace must be watched closely to 
see that the blast nozzles do not burn off, due to a temporary 
stoppage of the water, or that the furnace does not become 
clogged and allow a considerable quantity of the melt to collect. 
Either of these conditions is likely to result in severe explosions. 
The reaction which takes place in the smelter is 

Na 2 S0 4 + 4C = Na 2 S + 4CO. 

This is to a certain extent reversible as the oxygen supplied in 
the air blast oxidizes a small amount of the sulphide back to 
sulphate. For this reason it is not possible to produce a liquor 
entirely free from sulphate, the proportion depending on con- 
ditions in the smelter. The melt, if rich in sulphide, is of a red- 
dish color. The composition of various samples is as follows: 1 



Authority 



M. Muller 

W. Schacht. ........ 

Klason and Segerfelt 



Kgs. sul- 
phate per 
100 kgs. 
melt 



23-7 
11 .0 
8-10 
8-10 
20-22 
20-22 
20-22 



Composition of melt in per cents 



Na 2 CO ; 



56.60 
71.40 
80.26 
74.20 
59-42 
62 .07 
68.37 
61.73 



NaOH 



0.40 
O.50 
I .04 

1 .60 
0.20 

2 .20 

3-5° 



Na 2 S 



22 .60 

II .60 

7-i5 

9-5° 

14.00 

17-75 
13-75 
21.50 



Na 2 S0 3 



7-33 



NazSO, 



Insol- 
uble 



* Papier-Fabr., ign, 9, 1093-1099. 

Beveridge 2 gives the relationship between the melt, its solu- 
tion, and the causticized liquor as follows: 

1 Kirchner: Das Papier, 105, 279. 

2 Beveridge: Paper, 1918, 22, 21. 



*► 



REDUCING ODORS 



151 



Melt, per cent 



Solution of 

melt, grams 

per liter 



Causticized 

liquor, grams 

per liter 



Na 2 C0 3 

Na 2 S 

Na 2 S0 4 

NaOH 

Si0 2 

Insol. in water. 



62 .44 

26.96 

4.26 



2-3S 
6.18 



212.85 

104.17 

iS-84 



13-8 
28.7 
7.92 



From the smelting furnace the melt flows in a red hot con- 
dition to dissolving tanks containing water or the dilute washings 
from the lime sludge in the causticizing room. When the solu- 
tion has reached the desired density it is discharged into the 
causticizing system. This solution generally has a greenish tint 
from which it is termed " green liquor " to distinguish it from the 
" white liquor " obtained after causticizing. The dissolving 
tanks must be cleaned out occasionally because a certain amount 
of mud collects in them; this mud should be used in the caus- 
ticizing system in order to utilize the soda which it contains. 

The gases from the recovery furnaces have been analysed by 
Klason x and found to contain 13 mgs. of methyl mercaptan and 
4 mgs. of hydrogen sulphide per cubic meter. Careful blowing 
off from the digester reduces this by about one-third by removing 
more from the black liquor. The gases from the calciners can- 
not be washed commercially on account of the great size of the 
scrubbers required and the slight solubility of the impurities in 
water. On account of their great dilution only a small part 
could be burned by passing under the grates of the boilers. In 
order to reduce the formation of bad odors to a minimum the 
digesters should be blown off until the condensed distillate has 
no odor, the black liquor should be evaporated to such a point that 
it will not cool the fires enough to cause distillation or incomplete 
combustion, and the calciner should be given plenty of air. Lead 
acetate paper may be used as a test in controlling the running of 
the calciner. 

1 Klason: Papier Ztg., 1908, 33, 3619. 



152 THE SULPHATE PROCESS 

The methods for the analysis of the liquors and the recovered 
ash in the sulphate process are more complicated than for similar 
products in the soda process. The following procedure for white 
liquor has been worked out in the Forest Products Laboratory l 
and found to be accurate except in the presence of polysulphide. 

(a) Total Alkali. 

Two c.c. of the liquor are titrated with half normal acid using 
methyl orange as. an indicator. This gives the acid equivalent 
to the Na 2 C0 3 , NaOH, Na 2 S and \ Na 2 S0 3 . 

(b) NaOH and Na 2 S. 

To 2 c.c. of the solution contained in a 100 c.c. flask add 20 c.c. 
of a 10 per cent solution of BaCl 2 and make up to the mark with 
boiling distilled water; shake for a few minutes and allow to 
settle; cool and draw off 50 c.c. of the clear liquid and titrate 
with half normal acid, using methyl orange as indicator. 

(c) Sodium sulphide + Na 2 S 2 3 + Na 2 S0 3 . 

Find by trial the approximate amount of standard iodine 
necessary to react with 2 c.c. of the liquor. Using about half a 
c.c. less than this amount of iodine in 200 c.c. of water add 2 c.c. 
of the liquor, acidify with acetic acid and complete the titration 
with iodine using starch as an indicator. This shows the iodine 
equivalent to the Na 2 S, Na 2 S 2 3 and Na 2 S0 3 . 

id) Na 2 S 2 3 + Na 2 S0 3 . 

To 5 c.c. of the solution in a 250 c.c. graduated flask add an 
excess of an alkaline solution of zinc chloride; make up to the 
mark, shake for a few minutes, and allow to settle; draw off 
50 c.c. of the clear solution, and neutralize with sulphuric acid 
using methyl orange as an indicator. Titrate this solution with 
tenth normal iodine using starch as indicator; decolorize by add- 
ing one drop of sodium thiosulphate solution and titrate to neu- 
trality with tenth normal sodium hydroxide. The number of c.c. 

1 Paper, Feb. 23, 19 16, p. 30. 



METHODS OF ANALYSIS I53 

multiplied by 0.0042 gives the amount of Na 2 S0 3 in the sample 
and this figure divided by 0.0063 gives the iodine value of the 
sodium sulphite. Subtract this from the iodine titration previ- 
ously obtained, which will give the iodine equivalent to the so- 
dium thiosulphate present. 

Calculations. 

c -d gives the c.c« of iodine for sodium sulphide. 

a - b gives the c.c. for Na 2 C0 3 and § Na 2 S0 3 . 

The titration in (b) expressed as Na 2 0, minus the sodium 

sulphide as Na 2 0, gives the Na 2 equivalent to the NaOH 

present. 

This same procedure may be employed for the examination of 
the recovered ash in which case 50 grams of the sample are dis- 
solved in about 400 c.c. of freshly distilled water and after shaking 
repeatedly for two hours made up to 500 c.c. 

This does not include the determination of Na 2 S0 4 which may 
be accomplished by acidulating a measured volume of the solu- 
tion with HC1, boiling till all H 2 S is driven off and then pre- 
cipitating the sulphate with BaCl 2 . The BaS0 4 is filtered off, 
washed, ignited and weighed and from this weight that of the 
Na 2 S0 4 may be calculated. 

For a quick method of analysis for the control of the cooking 
liquor Heuser 1 recommends the following: 

Dilute 10 c.c. of the liquor to 100 c.c. 

(1) Treat 10 c.c. of the dilute liquor with an excess of — iodine 

10 

solution and determine the excess with — thiosulphate using 
starch as an indicator. Calculate to Na 2 S. 

(2) Heat 10 c.c. of the dilute liquor with an excess of — Ha 2 S0 4 

10 

till the odor of H 2 S is gone and then titrate back with — Ba(OH) 2 

10 
using phenolphthalein as indicator. This gives Na 2 S, NaOH and 
Na 2 C0 3 . 

1 Private communication. 



154 THE SULPHATE PROCESS 

(3) Treat 10 c.c. of the dilute liquor with 10 per cent BaCl 2 

N 
solution and titrate with — H 2 S0 4 . This gives NaOH and Na 2 S. 

10 

Calculations. 

(3) - (1) = NaOH. 
(2) - (3) = Na 2 C0 3 . 
(1) = Na 2 S. 

Moe l uses a silver nitrate solution containing 87.89 gms. 
AgN0 3 per liter for determining sulphides. When 1 c.c. is 
titrated the c.c. of AgN0 3 used represent pounds of Na 2 S per 
cubic foot of liquor. He gets the end point directly in the solu- 
tion by shaking to coagulate the silver sulphide, and noting the 
point at which no further precipitate is formed by a drop of the 
silver nitrate. 

Oliver 2 works in a somewhat similar way but uses an ammoni- 
acal silver nitrate solution. The liquor to be tested is filtered, 
made ammoniacal and boiled. The end point is determined by 
filtering, adding more silver nitrate and repeating till a drop 
causes only a slight opacity. 

The examination of black liquor for total alkali may be per- 
formed exactly as in the case of liquor from the soda process. The 
method for caustic soda, given under the soda process, if applied 
to sulphate black liquor will show both the caustic soda and the 
sodium sulphide present so that a correction for the latter is 
necessary. 

For the determination of sodium sulphide in black liquor the 
Forest Products Laboratory recommends the following method: 

Prepare a standard zinc solution by dissolving 16.746 grams of 
pure zinc in a small excess of nitric acid and adding ammonia 
till the precipitate formed is completely redissolved. The solu- 
tion is diluted to 2000 c.c. and enough ammonia must be present 
to keep the zinc from precipitating at this dilution. 

As indicator use a solution of nickel ammonium sulphate made 
alkaline with ammonia. 

1 Paper, Aug. 12, 1914, p. 19. 2 Paper, July 22, 1914, p. 20. 



METHODS OF ANALYSIS 155 

For the determination 50 c.c. of black liquor are diluted to 
1000 c.c. and 20 c.c. taken for the test. This is diluted to about 
100 c.c. and the zinc solution run in from, a burette. The end 
point is determined by noting whether a precipitate of black NiS 
is formed when a little of the solution being titrated is added to 
three drops of the ammoniacal NiS0 4 solution on a spot plate. 

Each c.c. of the zinc solution equals 0.010 grams Na 2 S. 



CHAPTER VI 
THE SULPHITE PROCESS 

The first patent relating to the use of sulphurous acid in pre- 
paring pulp from wood was that granted to B. C. Tilghman in 
1867. 1 This was followed in 1869 by a supplementary patent 
covering the treatment of fibrous materials at ordinary pressures, 
and it is upon these two patents that subsequent modifications 
of the process are based. The specifications of the original 
patent show that Tilghman had worked out his process in an 
experimental way with great care and thoroughness and that he 
fully understood all its possibilities. In its practical application, 
however, difficulties of an engineering nature arose which proved 
too serious for him to overcome. 

After his failure the process was taken up by Ekman and Fry in 
Sweden, by Mitscherlich in Germany, by Francke, Graham, 
Ritter, Kellner and numerous other investigators and manu- 
facturers and the engineering difficulties were gradually over- 
come so that finally the process was established on a firm footing. 

Theory of the Sulphite Process. Probably the best explana- 
tion of the sulphite cooking process is that it is primarily a hydro- 
lytic splitting of the cellulose-lignin esters followed by secondary 
decompositions of the lignin. Water alone at high temperatures 
will hydrolyze lignocellulose rendering part soluble, but in the 
presence of an acid, such as sulphurous acid, the reaction pro- 
ceeds much more rapidly and at a lower temperature. For- 
tunately cellulose itself is comparatively stable under such condi- 
tions but that it is by no means unattacked has been shown by 
Tauss and others. When a substance is present which will com- 
bine with the products of hydrolysis and remove them from the 

1 U. S. Pat. 70,483, Nov. 5, 1867. 
1S6 



WOOD AND ITS PREPARATION 1 57 

sphere of action the reaction will proceed to the limit fixed by the 
constitution of the lignocellulose. Such substances are the 
sulphites which during the reaction form true chemical com- 
pounds with the aldehydic products of decomposition. The 
organic acids formed during the decomposition of the lignin also 
combine with the sulphites and thereby set free an equivalent 
amount of sulphurous acid. During the latter part of a cook 
this causes a steady increase in the amount of gas which necessi- 
tates " blowing off " to prevent too great pressure. 

According to Klason * lignin is a glucoside-like body of which 
a part is sugar-like or cellulose while the other part is of an 
aromatic nature. This contains an oxypropylene group, 
-CH= CH - CH 2 OH, 

as well as methoxyl, hydroxyl and aldehyde groups. It is closely 
related to coniferyl alcohol. In the sulphite process sulphurous 
acid is taken into the double bond 

= C = C 

II + H 2 S0 3 = I 
= C = CS0 2 OH 

and forms the calcium salt of lignin sulphonic acid, 

CisHjgOsSCa \. 

Secondary reactions may cause the formation of calcium sul- 
phate, either from the decomposition of the calcium bisulphite 
according to the reaction : 

3 Ca (HS0 3 ) 2 = 3 CaS0 4 + H 2 S0 4 + S 2 + 2 H 2 

or from reduction of tannin with consequent oxidation of sul- 
phurous acid. This latter reaction explains the difficulty in 
using wood rich in tannin. 

Wood and Its Preparation. One of the chief requisites for 
wood to be used in the sulphite process is freedom from any 
excessive amount of rosin, and of nearly equal importance is the 
even distribution of that which is present. If the rosin is local- 
ized at certain points the wood at those places will remain hard 

1 A. Klein: Papier Ztg., 1906, p. 474. 



158 THE SULPHITE PROCESS 

and will cause shives in the pulp from the portions which are 
easily reduced. 

In the sulphite process the liquor has not nearly the solvent 
power of the alkali used in the soda process and any bark, decayed 
portions or knots which go into the digester are likely to appear 
as dirt in the finished pulp. This applies to the light-colored 
inner bark if the product is to be used unbleached, since it takes 
on a dark color and shows in the pulp as dark fibres. For 
bleached pulp, however, this inner bark is harmless, since it 
bleaches quite as readily as the rest. 

The removal of the bark is accomplished practically in a num- 
ber of ways. Hand peeling in the woods is not so usual for 
spruce though it is quite general for the poplar used in the soda 
process. Disc barkers of various types are most commonly 
used; in these the log is held by hand or machinery against 
knives fastened to a rapidly revolving disc. These knives remove 
much wood as well as bark, particularly where the sticks are 
crooked. The amount of such loss depends on the size of the 
logs as well as the care with which the work is done; the sound 
wood lost may amount to 8 to 20 per cent of the original weight 
of the logs, in addition to the 8 to 10 per cent of true bark; the 
total loss, therefore, amounts to 16 to 30 per cent of the logs as 
received. The drum barker, which is a device to remove the bark 
by rubbing the logs against one another and the sides of the drum, 
saves all this loss of wood. It is, however, expensive to install, 
requires more power than other barkers to do the same amount 
of work, and in winter the water used in it has to be heated, which 
adds to the expense. This type of barker is suitable only where 
very clean pulp is not essential or where bleached pulp is to be 
made as it does not remove all the thin inner bark. It is best 
applied to wood which has been in the water two or three months 
as the bark is then more readily removed. Of the drum barkers 
the intermittent give better results than the continuous. 

With any system of barking the logs should be inspected on 
the conveyor as they go to the chipper, and any with bark remain- 
ing in cracks or around knots put at one side to be cleaned by 



WOOD AND ITS PREPARATION 



159 



hand. Some operators clean very little by hand but put the 
defective wood at one side to be cooked separately into second 
grade stock. This necessitates a very thorough cleaning up of 
all apparatus afterwards. 

The barked wood next goes to the chippers which should be 
run slowly enough to produce even chips. The length of chip 




Fig. 21. Pulp Wood Chipper 



depends on the method of cooking as well as the kind of wood. 
For hemlock they should be § to f inch long while spruce is 
chipped about as follows: 

For Mitscherlich unreachable i\ to if inches long. 

For quick cook, newsprint stock f to i inch long. 

For easy bleaching f to f inch long. 
The coarse chips are generally further reduced in size by some 
sort of crusher and are then screened to remove coarse pieces, 
which are rechipped, and sawdust, which goes to waste. The saw- 
dust from chipping should not amount to more than 3 per cent. 

The knots may be removed from the chips in several ways; one 
very successful process is to blow them against an inclined wire 



160 THE SULPHITE PROCESS 

screen through which the dust and fine material passes while the 
good chips slide down the screen and are collected on a conveyor. 
By proper adjustment of the air blast the knots, being heavier 
than the good chips, fall short of the screen and are collected by 
a separate conveyor. Another method, which also makes use of 
the difference in weight of the good chips and knots, is that of 
passing the dry chips through a trough of water. The good 
chips float and are removed by a conveyor which passes across the 
surface of the tank, while the knots, being heavier than water, 
sink to the bottom and can be removed by scrapers. 

Uniformity and cleanliness of chips are essential to clean pulp 
and good yield and all chips cooked in the same charge should be 
of one kind of wood and as nearly as possible of the same age and 
moisture content. Much difference of opinion exists as to the 
relative desirability of wet or seasoned wood. Many prefer dry, 
well seasoned chips, claiming more rapid penetration of the 
liquor and better yield; others x state that green wood or that 
which has lain in the water for some time is reduced more easily 
than seasoned wood. Experiments by the author tend to confirm 
this latter opinion, as in certain cases woods which could not be 
successfully treated dry readily yielded to the acid if they were 
saturated with water before cooking. 

The capacities of wood handling machinery vary enormously 
under the conditions of operation but they may be said to be 
approximately as follows. 

Circular and band saws up to 50 cords per hour. 

Drum barkers , 1-4 cords per hour. 

Disc barkers 1 . 2-1 . 4 cords per hour. 

Chippers 10-15 cords per hour. 

Flat screens yV cord per sq. ft. per hour. 

Liquor Making. The liquor or acid used in the sulphite 
process is an aqueous solution of sulphurous acid in which lime, 
or some other base, has been dissolved; the final result is there- 
fore a solution of the bisulphite of the base containing an excess 
of sulphurous acid. In practice this is prepared in two different 
1 Griffin and Little: Chemistry of Paper Making, p. 189. 



PREPARATION OF SULPHUR DIOXIDE l6l 

ways: by passing the gas through water in which the base is 
dissolved or suspended, or by bringing the gas into contact with 
comparatively large lumps of the carbonate of the base which 
are moistened by a continuous flow of water. The first effect of 
this treatment is the solution of the gas in water forming the true 
sulphurous acid: 

H 2 + S0 2 = H2SO3. 

This then attacks the base according to one of the following 

Ca (OH) a + H 2 S0 3 = CaS0 3 + 2 H 2 0. 
or • CaC0 3 + H 2 S0 3 = CaS0 3 + H 2 + C0 2 . 

If the base is soda or magnesia the sulphites stay in solution but 
if lime is used calcium sulphite is precipitated as fast as it is 
formed since it is very insoluble, one part requiring about 800 
parts of cold water for its solution. In the first method, working 
with milk of lime, the formation of sulphite continues until all the 
lime is precipitated; further passage of the gas then causes this 
to redissolve with formation of the bisulphite. When limestone 
or dolomite is used, as in the second method, its surface grad- 
ually crusts over with the sulphite which is again brought into 
solution as more gas is dissolved. Both of these reactions doubt- 
less take place simultaneously when there is a liberal supply of gas. 

Of the available bases for making sulphite liquor soda has the 
advantage of forming a stable bisulphite and the cellulose pre- 
pared with such liquor is very pure and easy to bleach. Magnesia 
possesses these qualities, but in a lesser degree, while lime is 
likely to make the fibre hard and harsh from formation of calcium 
monosulphite. 

Preparation of Sulphur Dioxide. Sulphur dioxide for use in 
the absorption system is prepared by burning either sulphur or 
iron pyrites and with proper care good results can be obtained 
by either method. The choice of the two processes depends to 
a great extent on local conditions, such as t^ie relative cost of the 
two materials, the possibility of disposing of the spent oxide 
from the pyrites, the floor space available, etc. ; it is much more 
of a financial problem than a technical one. 



162 THE SULPHITE PROCESS 

Sulphur burning was formerly carried on very largely in the 
retort type of furnaces into which the sulphur was fed through a 
door at one end. This caused gas of irregular composition due 
to the sudden rush of cold air into the furnace and through the 
apparatus. This type of furnace was suitable for very pure sul- 
phur, particularly Sicilian, but when there was a tendency for 
the sulphur to form an oily surface scum during burning good 
results were not obtained. This trouble can be overcome by 




Fig. 22. Rotary Sulphur Burner 

installing rakes which travel slowly back and forth, breaking up 
the scum and presenting fresh surfaces for combustion. With 
this device the flat burners give excellent results. 

Modern sulphur burners are of two quite dissimilar forms — 
one a horizontal rotary furnace and the other vertical and sta- 
tionary. In the rotary burner, illustrated in Fig. 22, the sulphur 
enters from the hopper at the front end and gradually works 
toward the back. As the burner revolves the sulphur is carried 
up the sides and thus presents a large and continually renewed 
surface for combustion. A highly successful modification of the 
sulphur feed is to introduce it in the molten condition through a 
pipe entering at the axis of the burner. A continuous supply of 



* 



PREPARATION OF SULPHUR DIOXIDE 



163 



molten sulphur may be obtained by placing the crude sulphur 
in a steam jacketed tank and also surrounding the delivery pipe 
with a steam jacket so that the sulphur will not solidify before it 




Fig. 23. Vesuvius Sulphur Burner 
Courtesy of Valley Iron Works Company 

reaches the burner. Users of this type of burner claim that it is 
the best if it is fitted with self-feeding device and a large com- 
bustion chamber because it makes stronger and more uniform 
gas and starts and stops very quickly in case of shutdowns. 



164 



THE SULPHITE PROCESS 



"¥" 




Fig. 24. Vesuvius Sulphur Burner, Sectional View 
Courtesy of Valley Iron Works Company 

The stationary type of burner is illustrated in Figs. 23 and 24. 
It consists of a vertical cylinder lined with fire brick and fitted 
with four combustion trays or shelves. The sulphur is introduced 
through a melting chamber at the top and flows downward from 



PREPARATION OF SULPHUR DIOXIDE 165 

one tray to the next. The ash and residue from the sulphur col- 
lect at the bottom and if at any time they accumulate on the 
shelves they can be flushed downward by a sudden increase in the 
sulphur feed. This burner has no moving parts and therefore 
requires no power. The makers claim that a burner a little less 
than 7 ft. high over all and occupying a floor space 6 ft. square 
has a capacity of 9 tons per twenty-four hours. It is the exper- 
ience of numerous operators that burners of this type are difficult 
to run satisfactorily. 

The most important factor in sulphur burning is the regulation 
of the air supply. One pound of sulphur requires for its complete 
combustion just one pound of oxygen, which is the amount con- 
tained in 53.8 cu. ft. of air. If much more air is admitted, and 
particularly if it contains much moisture, there is a formation of 
S0 3 and sulphuric acid which causes loss of both lime and sul- 
phur. According to Frohberg x the maximum formation of S0 3 
takes place at 400 to 500 C. while at 900 to 1000 C. it is again 
broken up into sulphur dioxide and oxygen. He recommends 
running the furnaces as hot as possible to produce rich gas which 
should then be at once sprayed with cold water to reduce its 
temperature to 90 to ioo° C. In one modern American mill the 
best temperature, measured at the outlet of the combustion 
chamber, is considered to be 620 C, while variations from 480 
to 68o° C. sometimes occur. 

According to Cosier 2 poor cooling may be responsible for 
excessive formation of SO3, weak cooking acid and low free SO2. 
Acid saturated with CaS0 4 may carry into the digesters as much 
as 55 lbs. per ton of chips. This is largely precipitated at the 
temperature of cooking and may cause poor penetration and 
necessitate a high temperature to finish the cook. The ehmina- 
tion of S0 3 can be assured by employing the Cottrell electrical 
precipitation process or filtering the gas through sawdust as 
recommended by Paulson. 3 

1 Chem. Ztg., 1914, 38, 126. 

2 Cosier: Paper, 1918, Feb. 13, p. 19. 

3 Paper, 1917, 21, Oct. 3, p. 32. 



1 66 THE SULPHITE PROCESS 

Any overheating of the burner is likely to cause vaporization 
of unconsumed sulphur which passes along with the gases until 
it reaches the colder portions of the system where it condenses. 
Sublimation of sulphur also occurs when too little air is admitted 
after the burner has become thoroughly heated up since there is 
then too little oxygen present to combine with all the sulphur 
vapor. The sublimation of sulphur is likely to lead to the 
formation of thiosulphuric and polythionic acids which at the 
temperature of cooking again break down with the liberation of 
sulphur. Free sulphur may also appear in the acid from direct 
contamination with sublimed sulphur. Klason claims that a liquor 
may contain as much as 250 mgs. per liter of sulphur as thiosul- 
phuric acid before sulphur is formed in the digester and as under 
normal conditions the fresh liquor contains only about 3 mgs. per 
liter of sulphur the danger from this source is not very great. 

The conditions under which a burner is working may be judged 
from the appearance of the flame. When operating satisfac- 
torily it is blue, sometimes tipped with white; if it shows brown 
fumes of unconsumed sulphur vapor it indicates that the furnace 
is too hot, probably from the use of too much air, and that there 
is danger of sublimation. 

Attached to, or immediately adjoining, nearly every type of 
sulphur burner is a combustion chamber which the gas enters as 
soon as it leaves the burner proper. This is so arranged that more 
or less air can be admitted at will through appropriate dampers 
and in this way sublimed sulphur carried along from the burner 
can be completely burned to sulphur dioxide. 

The burning of pyrites in the old type of burners was con- 
siderably more difficult to control than the burning of sulphur 
and it could be worked advantageously only where the burners 
could be grouped together in sufficient numbers to insure gas of 
even composition. Many of these difficulties have been over- 
come by modern mechanical furnaces of which the Herreshoff fur- 
nace is a type. These burners (see Fig. 25) usually have five 
shelves over which the pyrites is raked in succession by mechan- 
ically operated rakes. The shafts and arms are hollow and are 



PREPARATION OF SULPHUR DIOXIDE 



167 



cooled by a current of air supplied by a fan; part of the hot air 
thus produced is used in the lower parts of the chamber and 
materially assists combustion. The heat produced by the oxida- 
tion of the sulphur and iron is sufficient for carrying on the opera- 
tion and once the furnace is in good working condition no fuel is 
required. The spent pyrites or cinders leaves the furnace with 
I per cent to 4 per cent of sulphur. The separation of dust is 




Fig. 25. Herreshoff Pyrites Burner 

particularly important where pyrites is used. This was formerly 
done by passing the gas through long chambers of large area so 
that the velocity of the gas should be slight. In modern practice 
it is more successfully accomplished by passing the gas through 
towers into which water is sprayed; this not only removes dust 



i68 



THE SULPHITE PROCESS 



but also takes out SO3 and cools the gas. Provided the wash 
water is discharged at 175 F. (8o° C.) the loss from dissolved 
SO2 is very slight. 

The gas from sulphur burners operating under satisfactory 
conditions generally contains 14 to 18 per cent of S0 2 by volume; 
the maximum which it can possibly contain is 21 per cent. In 
the case of pyrites the theoretical maximum is 16.2 per cent of 
SO2 and it generally runs about 10 to 14 per cent. As a rule when 
burning sulphur about 2 to 3 per cent is converted into S0 3 while 
with pyrites as much as 13 per cent may be lost in that way. 

After leaving the combustion chambers the gas is conveyed 
through iron pipes to the coolers. Up to this point the gas is hot 
and dry and has little action on iron but for the cooler and all 
pipes beyond lead should be used. The cooler generally con- 
sists of lead pipes through which the gas passes back and forth. 
These pipes are placed in a trough through which water flows, or 
are so arranged that a thin film of water trickles over them. The 
cooling surface should be about 15 sq. ft. per ton of daily produc- 
tion which is sufficient to bring the gas nearly to the temperature 
of the water in summer. In winter the gas should be cooled to 
about 55 F. (12.8 C). Regular and uniform cooling of the gas 
is very important as the rate of absorption and the quantity of 
gas dissolved depend very largely upon the temperature. The 
following table 1 shows how rapidly the quantity of gas absorbed 
decreases with rise in temperature. 





1 vol. of water dis- 


1 vol. of solution 


Temperature 


solves SO2 


contains SO2 


Degs. C 


Vols. 


Vols. 





79-79 


68.86 


10 


56.65 


SI-38 


20 


39-37 


36.21 


30 


27.16 


25.82 


40 


18.77 


17 .OI 



Absorption Apparatus. The apparatus in which the bisul- 
phite solution is prepared depends on whether the base is used 

1 Schonfeld: Ann., 95, 5. 



ABSORPTION APPARATUS 



in suspension or in lumps of con- 
siderable size. In the first class 
come the apparatus of Partington, 
McDougall, Frank, Burgess, Steb- 
bins, Barker, etc., while in the 
second class are the systems of 
Flodquist, Mitscherlich, Kellner, 
Ekman, Jenssen, etc. As the 
tower is the oldest and in some 
ways the simplest form of absorp- 
tion apparatus it will be con- 
sidered first. 

The essential feature of the 
Mitscherlich system is a high 
tower, usually circular in section 
and built of wood or of cement 
lined with acid resisting tile. 
They vary from 6 to 10 feet in 
diameter and from ioo to 150 feet 
in height and generally taper 
slightly toward the top. Fre- 
quently four or more towers are 
built together and the whole sur- 
rounded with a wooden structure 
with stairs, platforms and stone 
hoist. A water tank, supplied 
with cold water, surmounts each 
tower. The stone is supported 
on strong oak beams placed about 
6 to 10 ft. from the bottom and 
below these, and about a foot 
above the acid outlet, are other 
beams set close together to catch 
pieces of stone which pass the 
upper timbers. Frequently the 
tower is divided into sections 




170 THE SULPHITE PROCESS 

by timber gratings to assist in the filling and the regulation of the 
absorption. Some towers act as chimneys and no artificial 
draft is necessary while with others it is desirable to place a fan 
between the burners and the towers and a steam exhaust at the 
top of the towers. 

Ritter-Kellner towers are constructed in pairs; the acid from 
the bottom of one is pumped to the top of the second while the 
gas from the top of the second is led into the base of the first. 
These towers are smaller than the Mitscherlich towers and have 
the advantage of avoiding undue loss of gas. 

Further development along this same line is in the direction 
of the multiple tower system where towers about 20 ft. high are 
worked in groups of six to eight. The acid passes through these 
in succession in one direction and the gas in the other. This 
system is easy to charge with stone, and permits regulation of 
the gas temperature between towers, which is important in 
maintaining a constant ratio of base to acid. Its disadvantage 
lies in the necessity for so many small acid pumps. Such a 
system is cheaper to install but more costly in repairs than the 
high tower system, and the latter is replacing all others in 
European plants. 

In any of these systems the towers are filled with lumps of 
limestone or dolomite. In European works a special soft lime- 
stone is preferred but sufficiently pure material of this nature is 
not available in this country and ordinary dense stone is used. 
A stone low in magnesia and as free as possible from dirt, iron and 
silica is preferred. Since marble is practically all calcium car- 
bonate and is of uniform structure it is highly satisfactory for use 
in towers. A typical analysis of a suitable stone is as follows: 1 

Per cent 

Loss on ignition 43 ■ 6 3 

Iron and alumina o. 74 

Calcium oxide 54- 10 

Magnesium oxide 0.82 

Silica Q-59 

99- 88 
1 Cooper: Paper, 1918, 22, 721. 



ABSORPTION APPARATUS 171 

The water is discharged over the stone at the top by spray 
pipes or some similar device and in passing downward forms a 
thin film on the surface of the lumps. In order that it may be 
properly distributed the inside of the tower is fitted with wooden 
rings at intervals which prevent the water from running down 
the walls without moistening the stones. The gas from the 
burners enters the base of the tower under the grating and pass- 
ing upward over the moist limestone is very rapidly absorbed by 
the downward flowing film of water. 

In working with tower systems several difficulties are likely to 
be encountered. It is hard to secure a uniform distribution of 
the water as it descends the tower or a proper spread of the ascend- 
ing gas. This tends to form channels which increase rapidly 
after their first appearance. The lower lumps of stone are in 
contact with the strongest gas and so dissolve more rapidly than 
those in the upper part of the tower; this tends to form arches 
which finally break, letting the stone above settle so compactly 
that it may impede the passage of the gas. This trouble is over- 
come in modern installations by tapering the tower toward the 
top, by dividing it into sections which are packed with stone 
separately and by proper periodical inspection. In the lower 
part of the tower crusts of sulphate or of monosulphite of lime 
sometimes almost stop the flow of gas; the latter is particularly 
apt to form if the gas is weak or insufficient water is used. Irreg- 
ular acid is also likely to result if the temperature varies since, 
as already shown, the solubility of the gas decreases rapidly with 
rise of temperature while at the same time the base is much more 
quickly dissolved thus changing the proportion between free and 
combined acid. 

Apparatus for use in acid making by the other system, where 
the base is in solution or suspension, generally consists of a 
series of tanks with accompanying piping or in other installations 
of towers divided into sections by partitions. A frequent 
arrangement consists of three tight tanks fitted with agitators 
and with pipes so arranged that the gas enters the bottom of the 
first tank and passes upward through the solution; from the 



172 



THE SULPHITE PROCESS 



















■V 
+■> 

a> 

SB 

5 
















1 —~ 











ABSORPTION 

upper part of this tank the un- 
absorbed gas passes to the 
bottom of the second and so 
on through the system. The 
gas may be either forced in 
under pressure or caused to 
pass through by an exhaust 
fan attached to the last tank. 
It is general to place the tanks 
at different levels so that after 
drawing off the finished acid 
from the first tank the contents 
of the second and third may 
each be run down one stage by 
gravity. Fresh milk of lime 
is charged into the third, or 
upper, tank, and the finished 
liquor leaving the lower tank 
should be quite clear. 

The Burgess and the Barker 
systems are examples of the 
towerlike form of tank appa- 
ratus. The Burgess apparatus 
is generally one high tank di- 
vided into three parts by hori- 
zontal partitions. It is fitted 
with a hollow shaft and arms 
through which the gas passes 
and is mixed with the milk of 
lime. The Barker apparatus 
illustrated in its relation to the 
other equipment in Fig. 27, is 
a high tank divided into three 
or more compartments by hori- 
zontal perforated partitions. 
The construction of the tower 
is shown in Fig. 28. The milk 



APPARATUS 

5ecr/oN A- A 



173 




Qcmcnt Qacxinq Sreci. tank Aoo 'psoof Brick 

Fig. 28. Barker Tower, 
Sectional View 



174 



THE SULPHITE PROCESS 



of lime enters the upper compartment in a continuous flow and 
meets the gas bubbling up through the perforated false bottom. 
The weak liquor passes through an overflow pipe to the next 
compartment where it absorbs more gas, and so on through the 
four sections. From the lowest one it flows onto a distributing 
plate which allows it to trickle down into the absorbing tower 
where it meets strong gas and is strengthened to the desired 
composition. The gas enters near the bottom under a perforated 
distributing plate above which is the absorption tower filled with 
stoneware filling to increase the surface exposed. This appa- 
ratus, as well as any good tower system, working in conjunction 
with a proper reclaiming system, will produce an acid with i 
per cent combined and up to 6 per cent total S0 2 . 

The quality of the lime or dolomite used for liquor making is 
of the greatest importance and its value increases with the 
amount of magnesia which it contains. For use in milk of lime 
systems it should be well burned, should slake easily and should 
be as free as possible from silica and iron. Air slaked or poorly 
burned limes are not so readily acted on as those of good grade 
and they are likely to vary so in composition that it is almost 
impossible to keep the correct proportion of base to acid. The 
following analyses show the composition of several extensively 
used limes from different parts of the country. 



Calcium oxide, CaO 

Magnesium oxide, MgO 

Alumina and ferric oxide, A1 2 3 and Fe20 3 

Sulphur trioxide, SO3 

Insoluble in HC1, sand, etc 

Silica soluble in acid, Si02 

Loss on ignition, H 2 0, CO2, etc 



Massachu- 
setts 



Per cent 
56.02 
40.10 

0.57 
O.II 

0.94 
0.47 

i-43 
99-64 



Ohio 



Per cent 

5 8.6l 

40.25 

O.I2 

0.1S 

0.07 

0.15 

99.86 



New- 
Brunswick 



Per cent 

55-96 

37-98 

I.23 

0,16 

I-5I 



99-65 



It frequently happens that lime of the above quality cannot 
be obtained on time so that it is necessary to use high calcium 



ABSORPTION APPARATUS 1 75 

lime for a certain period. It has been found by experience with 
the Barker system that this causes no serious inconvenience nor 
does it require any radical change in the cooking system. The 
opinion seems to be gaining ground that a high calcium lime can 
be used in the milk of lime system with practically the same results 
as with dolomitic lime. 

Lime for use in the absorption system is first slaked either in 
tanks provided with agitators or in troughs. One authority 
recommends a tank with a perforated plate on which the lime is 
dumped after filling the tank with water to one inch above the 
surface of the plate. The lime is sprinkled on top with water 
and when it steams freely is quickly covered with water. The 
milk of lime produced is diluted sufficiently so that it can be 
strained through brass sieves of 60 meshes to the inch and the 
strained material run to storage tanks fitted with agitators where 
it is diluted to the proper consistency. The milk of lime must 
be cold when it goes to the absorption system. According to 
Beveridge x the finished milk of lime has a specific gravity of 
1.0075 and contains 6.31 gms. per liter of CaO and 4.19 gms. 
per liter of MgO. This corresponds to about 91 lbs. of lime of 
the composition given to a thousand gallons of acid. As the lime 
is never entirely dissolved and some is lost as sulphate and mono- 
sulphite in cleaning the apparatus more than the above quantity 
has to be used, the amount depending on the quality of the lime, 
the type of apparatus, etc. 

There is still much dispute as to the relative advantages of the 
tower and milk of lime systems. The latter are no longer com- 
mon in Europe where towers are generally employed, but they 
are much used in America. The advocates of the tower systems 
claim that they are simpler to operate, require less power and cost 
less for upkeep. The cost of lime is also less as the unburned 
stone is cheaper than burned lime. Obermanns 2 states that 
towers require 50 to 60 horse power as compared with 225 horse 
power for a three tank system, and that the sulphur per ton of 

1 Beveridge: Paper Makers' Pocket Book, p. 99. 

2 Obermanns: Paper, 1918, Feb. 13, p! 100. 



176 THE SULPHITE PROCESS 

pulp is 240 lbs. as against 300 lbs. for the tank system. For a 
100-ton mill these savings, together with that for the cheaper 
lime, would amount to $42,000 to $52,000 per year. Textor 1 
compared the systems from a thermochemical standpoint and con- 
cludes that an acid of 2.00 per cent free and 1.60 per cent com- 
bined S0 2 will entail a rise of 6.4 C. if made in towers from cal- 
cite, and 16.1 C. if made in a milk of lime system from a high 
magnesia lime without the use of steam in slaking or of cooling 
water in making up . the tanks. Considering the claim that 
towers produce stronger acid it is to be noted that they operate 
at nearly atmospheric pressure whether the gas is passed through 
by pressure or vacuum. Tank systems, such as the Barker, gen- 
erally operate by means of a vacuum pump and if this were 
changed to force the gas through under pressure the strength of 
the acid would be increased by 1 5 to 20 per cent. 

The losses which occur in making sulphite liquor are those due 
to dirt, ash and moisture in the sulphur, to sublimation, and to 
the formation of sulphuric acid. The loss from the first four 
causes should never exceed 5 per cent, but that from formation 
of sulphuric acid is likely to amount to very much more unless 
careful control is maintained. The formation of monosulphite, 
which is removed with the sediment in the storage tanks or in 
cleaning the absorption system, may also cause considerable loss. 
Such wastes should be examined before being thrown away as 
it often pays to work them over. 

The acid made in either the tower or the tank system varies 
very widely in different mills according to the kind of fibre being 
made and the method of enriching the liquor with the relieved or 
recovered gas. There is no essential difference, however, between 
the two systems with regard to the liquor produced. Harpf 2 
gives the composition of liquor of 4.5 Be. from Mitscherlich 
towers as follows: 

Per cent 

Total S0 2 3-397 

Free S0 2 2. 098 

Combined SO2 1 • 299 

1 Textor: Paper, 19 18, Feb. 13, p. 60. 2 Harpf: Dissertation, 1892. 



PUMPING AND STORAGE 1 77 

The acid from either tower or tank system is stated by Thorne 1 
to have the following composition before being enriched by the 
recovered gas. 

Per cent 

Total S0 2 2. 60 

FreeS0 2 ... 1.60 

Combined SO2 1 • 00 

The finished acid when ready for the digesters is also very variable 
in strength. From reports on a number of American mills the 
following figures have been selected as representative: 



Total S0 2 

Free S0 2 

Combined SO2 



I 


2 


3 


4 


Per cent 


Per cent 


Per cent 


Per cent 


4-3° 


4.09 


5-50 


3-8o 


3.10 


2.46 


4-5° 


2.40 


I .20 


1.63 


1 .00 


1 .40 



Per cent 
6.24 
5.22 
1 .02 



Acid of the strength of No. 5 can only be obtained during warm 
weather bjf employing artificial refrigeration; in this particular 
case the temperature of the acid ready for the digesters was 72 F. 

(22. 2° C). 

Pumping and Storage. Where the liquor is to be discharged 
directly into the digester, a steam injector may be used for 
transferring it, but if nothing is to be gained by heating the liquor 
an injector is too expensive and it also causes considerable loss 
of sulphurous acid. The best method of handling is with rotary 
pumps of acid-resisting bronze, which should be so placed that 
the acid flows to them under a slight head. If a pump is so 
placed that a foot-valve is necessary on the suction pipe continual 
trouble will be caused by the crystallization of monosulphite in 
the working parts. 

Storage tanks for liquor are generally of wood, either Southern 
pine or Douglas fir, without lining. They should be made tight 
with water or steam before any liquor is admitted so that no 
monosulphite may crystallize between the staves. The tanks 

1 Thorne: Pulp Paper Mag. Can., March 15, 1915, p. 173. 



178 



THE SULPHITE PROCESS 



should be covered to prevent escape of gas but the covers need 
not be perfectly air-tight since there is little loss in strength, 
either through escape of gas or Oxidation to sulphate, when the 
liquor is stored in quantity. The tanks should be fitted with 
gauge glasses to show the depth of liquid and the delivery pipes 
should draw from near the bottom but high enough to avoid 
sediment. The tanks should be so located that the sediment 
may be easily washed out when necessary. 

Digesters and Digester Linings. The acid liquor used in 
the sulphite process acts so destructively on iron that some form 
of lining is necessary to protect the digester shell. According to 
Griffin and Little x wrought iron suffers most severely, steel 
resists somewhat better and cast iron suffers least of all. Even 
the modern acid-resistant cast irons, which are extensively used 
in concentrating acids, have proved to be too easily attacked to 
be safe for use in the sulphite industry. Tests by the author on 
a number of such cast irons gave the following results: 





Loss in grams per square inch 




18 hours in 
' cold 


4 hours more 
at 90 C 


18 hours more 
in cold 


Ordinary cast iron 


O.6410 
0.2615 
O.2362 

0.327S 
O.5410 






Acid resistant No. 1 


0.1096 
0.0990 
O.2138 


O . 2030 
O.I 184 
O.1797 


Acid resistant No. 2 


Acid resistant No. 3 

Acid resistant No. 4 







Lead is the only common metal which satisfactorily resists the 
action of the acid liquor and this is due very largely to the 
formation of a surface film of insoluble lead sulphate which acts 
as a protective coating for the metal beneath. Lead, however, 
has certain properties which have prevented its successful use in 
digester lining in spite of the immense amount of time and money 
which have been spent in the attempt. Its coefficient of expan- 
sion is 0.0000297 while that of iron is only 0.0000123, so that on 

1 Griffin and Little: Chemistry of Paper Making, p. 232. 



DIGESTERS AND DIGESTER LININGS 1 79 

heating the digester the lead lining tends to become too large for 
the shell. This trouble is still further increased by the fact that 
lead which has been expanded by heat does not quite return to 
its original size on cooling but remains permanently larger. This 
causes " crawling" and " buckling" and cracks are apt to appear 
wherever short turns are made. There is also in vertical digesters 
a gradual creeping downward of the lead due to its own weight; 
this causes the upper part to become thinner and finally give 
way. Even uniting the lead to the iron by melting it on over a 
flux of zinc chloride, a true soldering process, did not prove 
entirely satisfactory. Griffin * states that such linings remained 
clean until about two hundred cooks had been made, then star- 
shaped defects showing cracks and hard crystals appeared and 
multiplied so fast that they could not be cut out and repaired. 
Finally black scabs of lead sulphide formed in large masses and 
the whole lining became worthless. Many other very ingenious 
methods for controlling the lead were tried but the task was 
finally given up as hopeless. 

Bronze digesters, built of cast sections, were tried at one time 
but were found to be more or less acted on by the liquor with 
the formation of black scales of oxide and sulphide of copper. 
Heating to the temperatures used in cooking considerably re- 
duces the strength of bronze and after several disastrous explo- 
sions the use of such digesters was abandoned. 

The Salomon-Briingger digester consisted of an inner shell of 
welded steel and an outer shell also of steel but riveted. The 
protective coating is obtained by admitting sulphite liquor into 
the digester which has been previously heated by steam in the 
jacket at about 40 lbs. pressure. This treatment causes the 
deposit of a hard, impervious crust of sulphite of lime which 
gradually increases in thickness with each succeeding cook. 
This coating did not prove to give adequate protection and the 
method was never in extensive use. 

The Mitscherlich lining is interesting as being the first in 

1 M. L. Griffin: J. Soc. Chem. Ind., 1898, 216-220. 



180 THE SULPHITE PROCESS 

which bricks were used. It consists first of a coating of tar 
and pitch applied directly to the shell, then a thin lining of 
sheet lead with the edges burned together and finally two 
courses of dense vitrified bricks with tongues and grooves. 
These were sometimes laid in Portland cement. 

The Preston lining consists of bricks of Scottish clay backed 
with a mixture containing clay and lead mixed to the consistency 
of bread dough with silicate of soda. This must be applied to a 
perfectly clean shell. 

Modern digester linings are generally of acid-proof bricks 
backed with cement next to the shell. The bricks are 2 to 3 ins. 
thick while the cement backing is about an inch thick. In some 
cases a lead lining is applied next the shell and upon this the ce- 
ment backing is laid. This is seldom done, however, as it is cus- 
tomary to pierce the digester shell with numerous small tell-tale 
holes so that the location of cracks in the lining may be approxi- 
mately known. The cement for the backing and pointing the 
first layer of bricks varies more or less in different localities. 
Steffanson 1 gives its composition as one part of cement, and two 
parts of crushed and sifted acid-proof brick with enough asbes- 
tos added to render it non-brittle; this is mixed to the desired 
consistency with 4 Be. silicate of soda. The last layer of bricks 
is pointed with litharge and glycerine and the bricks should be 
set half an inch apart to make repairs easy. Another formula 2 
for pointing the inner layer of bricks is 5 parts litharge, 2 parts 
cement and 3 parts quartz sand, all measured by volume. After 
mixing these materials dry, they are moistened with glycerine 
to the right consistency for use. This should be mixed in small 
quantities only and used quickly as the mixture retains the 
proper consistency for only a short time. Digesters pointed 
with this mixture have been operated up to eighteen months 
without repairs and in some cases the pointing has proved more 
durable than the bricks so that the latter have worn down, 
leaving a raised network of cement exposed. 

1 Steffanson: Pulp Paper Mag. Can., May 20, 1914, et seq. 

2 Private communication. 



DIGESTERS AND DIGESTER LININGS l8l 

The bricks used for digester lining should be very hard, dense 
and well annealed. If soft or under-burned they are apt to 
crack from changes in temperature and pieces then come away 
in the pulp. When tested by immersing in water for twenty-four 
hours they should not absorb more than 2 per cent of their 
weight. 

In general the form of digester used is that of a vertical cyl- 
inder with conical top and bottom. The total length is about 
three times the diameter, and the lower cone is about 60 degs. 
while the upper is about no degs. Digesters of other forms 
are of course used in some of the older mills and horizontal 
digesters are sometimes used for the Mitscherlich process. The 
size of digesters has gradually increased; formerly a capacity 
of 4 tons of fibre per charge was considered large while now 18 
tons or more is not uncommon. The following table by Cor- 
coran x gives the approximate capacities of sulphite digesters of 
standard construction and lined with the usual brick and cement 
lining: 

1 Corcoran: Paper, 22, 1918, 406. 



182 



THE SULPHITE PROCESS 



Capacity of Standard Sulphite Digesters with Standard Lining9 



Size of digester 
















Thickness 
of lining, 


Contents, 


Capacity- 
contents, 


Gallons of 








Cords of 


Diameter, 
ft. 


Height, 

ft. 


ins. 


cu. ft. 


tons fibre 


acid 


wood 


8 


24 


8 


610 


i-33 


3,000 


2.48 


8 


30 


8 


840 


i-75 


3,787 


3-24 


IO 


28 


8 


I-3I9 


2.66 


6,000 


4.96 


IO 


30 


8 


i>397 


2.90 


6,525 


5-34 


IO 


37 


8 


1, 850 


3-85 


8,663 


7.16 


IO 


40 


8 


2,024 


4-5o 


9,450 


7.81 


II 


30 


8 


1,672 


3-48 


7,330 


6.47 


II 


37 


8 


2,896 


4.60 


10,125 


8-37- 


II 


40 


8 


2,416 


5.00 


11,250 


9 30 


II 


42 


8 


2,563 


5-33 


12,000 


9.92 


II 


45 


8 


2,784 


5-75 


12,937 


10.69 


12 


3° 


9 


2,015 


4-i3 


9,282 


7.67 


12 


35 


9 


2,457 


5-io 


11,470 


9.48 


12 


40 


9 


2,879 


6 .00 


13,500 


11 .16 


12 


45 


9 


3,272 


6.80 


15,300 


11 .64 


12 


48 


9 


3,572 


7.40 


16,650 


13.76 


14 


38 


9 


3,8i9 


7-9o 


i7,775 


1464 


14 


42 


9 


4,320 


9.00 


20,250 


16.74 


14 


45 


9 


4,678 


9-75 


2i,934 


18.13 


14 


47 


9 


4,924 


10.50 


22,950 


18.97 


14 


48 


9 


5,046 


10.64 


23,625 


19-53 


14 


5o 


9 


5,392 


11 .20 


25,000 


20.83 


IS 


40 


10 


4,682 


9-75 


2i,934 


18.13 


IS 


42 


10 


4,964 


10.33 


23,250 


19.22 


IS 


45 


IO 


5,388 


11 .20 


25,200 


20.83 


IS . 


47 


IO 


5,671 


11.80 


26,550 


21.31 


IS 


5° 


IO 


6,096 


12 .40 


27,900 


22.06 


IS 


54 


IO 


6,652 


13-75 


3o,937 


25-57 


16 


45 


IO 


6,146 


12 .80 


28,800 


24.80 


16 


48 


IO 


6,680 


13-75 


30,937 


25-57 


16 


So 


IO 


6,952 


14.40 


32,400 


26.78 


16 


54 


IO 


7,598 


15.80 


35,55o 


29.38 


16 


60 


IO 


8,565 


17.80 


40,050 


33 -io 


16 


64 


IO 


9,210 


19.00 


42,750 


35-34 


17 


56 


IO 


9,o74 


18.80 


42,300 


34-96 


17 


60 


IO 


9,8i4 


20.25 


45,900 


37-94 


17 


64 


IO 


io,5S2 


21 .80 


49,050 


40.44 


17 


70 


IO 


11,660 


23.00 


5i,75o 


42.78 



The digester space required to produce 2000 lbs. of dry pulp 
is given by Steffanson as follows: 

Cu. ft. 

Mitscherlich process 400-425 

Quick cook process 450 

For easy bleaching pulp 475-500 



BOILING 183 

Boiling. The method of making a boil depends on whether 
the Mitscherlich or the quick cook process is being employed. 
The former is very generally used in Europe but in America is 
not nearly so common as the quick cook or Ritter-Kellner 
process. 

In the Mitscherlich process the digesters are either horizontal 
or vertical stationary boilers. The cooking is all done by steam 
admitted to coils of hard lead or copper pipe placed in the bot- 
tom of the digester. The standard procedure is to fill the 
digester with chips and then steam gently for several hours 
with direct steam, the water condensing being allowed to run 
to waste as a brownish liquid. Care must be used during this 
period to avoid steam pressure in the digester as temperatures 
much in excess of ioo° C. are likely to burn the wood. After 
steaming all valves except that leading to the liquor tanks are 
closed and the partial vacuum formed by the cooling of the 
digester and the condensation of the steam draws the cold 
liquor in rapidly. The object of this steaming and subsequent 
admission of cold liquor is to obtain thorough penetration of 
the chips by the liquor and so prevent floating and burning. 
Steam is now admitted to the coils and the temperature raised 
to no C. as rapidly as possible, although this may require as 
much as twelve hours because of the large size of the digester. 
When pressure is reached it is relieved by opening a valve for^ 
a few minutes to get rid of air; this is repeated two or three 
times in the next hour. Since the relief from Mitscherlich 
cooks contains no liquor no separator is necessary and the 
relieved gas can go at once to the reclaiming system. The 
temperature in the digester is gradually raised to about 120 C. 
which is maintained throughout the cooking period; during 
this time the pressure should not exceed 80 lbs. About an 
hour before the end of the cook the steam is shut off and the 
pressure gradually reduced to 50 lbs. by relieving gas; this 
must not be done too rapidly or the pulp may not be thoroughly 
reduced by the time the sulphur dioxide is gone. The contents 
of the digester are then discharged as usual. The old method 



1 84 THE SULPHITE PROCESS 

of emptying horizontal digesters was to admit cold water as 
soon as the liquor had been discharged, the object being to cool 
and wash the pulp which was finally removed by shovelling. 

The liquor used in the Mitscherlich process is about 3.5 to 
4.5 per cent total S0 2 with 0.9 to 1.24 per cent combined. The 
steam used in the coils is at 60 to 100 lbs. pressure: 75 lbs. in 
the coils gives about 90 lbs. in the digester. The actual time 
of cooking varies enormously in different mills. It was origi- 
nally about eighty hours, but this has been greatly reduced by 
raising the temperature of cooking and by using some direct 
steam to bring the charge up to pressure quickly. In this 
latter case space must be left in the digester to allow for con- 
densation. In modern practice the total time is about twenty- 
five to forty-five hours. Steffanson * states that for bleached 
pulp the cook is usually not more than twenty-four hours, while 
Beveridge 2 subdivides the time as follows for a digester which 
has to be emptied by hand. 

Hours 

Filling 2 

Steaming 4 

Filling with liquor 2 

Boiling 35 

Blowing off pressure 3 

Washing twice 6 

Emptying, etc : 5 

Total Jj 

The particular advantages of the Mitscherlich process are 
strong fibre and high yield because of the comparatively weak 
acid and the low temperature of cooking. It is stated by 
Bache-Wiig 3 that temperatures over 13 5 C. cause the forma- 
tion of hydrocellulose with consequent lower yield and loss of 
strength. 

The Ritter-Kellner, or quick cook process, in which the steam 
is blown directly into the digester, is the one most generally 

1 Steffanson: Pulp Paper Mag. Can., May 20, 19 14, et seq. 

2 Beveridge: Paper Makers' Pocket Book. 

3 Private communication. 



BOILING 185 

used in this country. The digester is usually charged with 
chips as fully as possible since the settling during the first part 
of the cook suffices to cover them completely with liquor. Steam- 
ing of the chips is seldom resorted to, though it is an advantage, 
as it drives out air, moistens the chips uniformly and makes 
better pulp. Moreover the partial vacuum formed in the 
digester when steam is shut off hastens the running in of the 
acid and makes it possible to perform this operation without 
removing the digester head. The most satisfactory point to 
admit the acid is at the bottom of the digester; if pumped in 
from below instead of on top of the chips it tends to loosen 
them up and helps the circulation. The steam inlet for cook- 
ing generally ends in a coil around the sides near the bottom 
and is perforated in such a way as to direct the steam up the 
sides, thus giving a downward current in the center and good 
circulation. There is also provided a small jet just at the 
bottom of the digester to cook the chips in the lower part of 
the bottom cone. 

The steam used in cooking may be superheated or ordinary 
saturated steam, the latter being used in far the greater num- 
ber of cases. Tests by Andrews 1 using superheated steam with 
a temperature of 500 F. at the digesters indicated that it gave 
a little more uniform product and that a somewhat stronger 
acid could be prepared. No difference in yield could be de- 
tected and the volume of liquor and the fuel required were the 
same as with saturated steam. 

The steam required for cooking is much greater than for a 
soda cook of a corresponding number of cords. This is due to 
the continual relief of gas and steam through the coolers into 
the recovery system. Andrews calculates the saturated steam 
for a 14 X 47 ft. digester holding 16 cords of rossed wood as 
about 60,000 lbs. per cook. In another plant with digesters of 
about the same capacity steam flow meter records during a 
period of four months showed that the average steam consump- 
tion per cook was 75,940 lbs. 

1 Andrews: Paper, Feb. 20, 1918. 



1 86 THE SULPHITE PROCESS 

In steaming a cook it is very important that the pressure be 
brought up slowly as otherwise a high temperature may be 
reached before the liquor has had time to penetrate the chips 
and their centers will be found hard and of a red or brown 
color. The time from the start until 75 lbs. pressure is reached 
varies in different mills from two to four hours. The pressure, 
however, does not afford a reliable indication of conditions 
within the digester since the actual steam pressure is augmented 
by that of the gas set free during boiling and in some cases the 
indicated pressure may be almost wholly hydrostatic due to the 
filling of the digester by condensation. The temperature is 
therefore the real factor to be watched and this should be taken 
at a point about one-third of the way down the digester. The 
best method of keeping track of the temperature is by means of 
some form of recording thermometer as this gives a permanent 
record of each cook from start to finish. 

No hard and fast rule for cooking can be given and each mill 
has its own particular method which is generally the result of 
gradual evolution rather than the application of scientific knowl- 
edge. As an example of the procedure in cooking easy bleach- 
ing pulp of high quality Steffanson * gives the following schedule: 
Steam in such a way as to reach 75 lbs. pressure in two to three 
hours; open relief and bring temperature to 240 F. (115.5 C.) 
in about an hour. Close both steam and relief valves for an 
hour and a half, then turn on steam and open relief very 
slightly. The maximum temperature of 300 F. (149 C.) should 
be reached in ten hours with the maximum pressure still 75 lbs. 
Now shut off steam but not relief, allow the pressure to drop to 
50 lbs. in one to two hours and discharge into the blowpits. 
At the end of the cook the liquor should test 0.05 per cent 
total S0 2 . If the cook is blown at a pressure much in excess of 
50 lbs. some partially cooked chips will be blown to pieces and 
cause shives. 

1 Steffanson: Pulp Paper Mag. Can., May 20, 1914, et seq. 



■ 



BOILING 



187 



In another mill making an easy bleaching sulphite for use 
in writing papers the following schedule is in effect: 

Bring to 78 lbs. pressure in three hours and then start relief. 

Bring temperature to 228 F. at 4th hour. 

Bring temperature to 246 F. at 5th hour. 

Bring temperature to 262 F. at 6th hour. 

Bring temperature to 278 F. at 7th hour. 

Bring temperature to 290 F. at 8th hour. 

Bring temperature to 298 F. at 9th hour. 

Start to reduce pressure when 5 c.c. of liquor require 2.7 c.c. 
of iodine and lower to 50 lbs. at blow, which is when 5 c.c. of 
liquor require 0.7 c.c. of iodine. 

Fig. 29 shows the general method of recording the conditions 




Time 
Fig. 29. Sulphite Cooking Chart 



within the digester during the cook. Observations are taken 
at frequent intervals and plotted on the chart in such a way as 



1 88 THE SULPHITE PROCESS 

to show the gauge, gas and steam pressures. This gives a graphic 
representation which can be followed easily by the workmen. 
The chart given is for a quick cook easy-bleaching sulphite. 
Fig. 30 is the temperature record taken during such a cook. 

During the progress of a cook the heat and the chemical re- 
actions taking place within the digester cause more or less gas 

^.., *$B _- — 1 — -—JJfy*' . 

4^ « .-■- \ IM^ 







^— $&&£ 







Fig. 30. Temperature Record of a Sulphite Cook 

to be evolved which results in a gradual building up of the pres- 
sure. This gas pressure is not injurious to the fibre provided 
the temperature is carried at the right point, but it is the general 
custom to reduce it by "relieving" or blowing off some of the 
gas either at intervals or continuously. Study by Schwalbe 1 of 

1 Schwalbe: Wochbl. Papier-Fabr., 1913, 44, 2786. 



RELIEVING GAS 189 

the relieved gases shows that when blown off at no° C. they 
contain no oxygen, indicating that all originally present in the 
digester has already been used up. He recommends relieving 
air when the temperature reaches 75 C. as the bisulphite is 
relatively stable at that temperature and the loss of gas will 
consequently be less. The relief at times also contains much 
liquor and for this reason it is sometimes passed through a 
separator of some kind so that the gaseous portion may be con- 
veyed to the liquor tanks to bring up the strength of the raw 
acid to the proper cooking strength. This recovery process is 
of the first importance in reducing the consumption of sulphur 
per ton of pulp. The amount of relief depends partly on the 
strength of the acid used since the stronger the acid the greater 
will be the amount of gas evolved on heating. The kind of 
cook, direct or indirect steam, and the temperature of cooking 
also have much influence on the amount of relief. If too much 
gas is blown off the pulp will be burned and whenever burned 
pulp is obtained and the temperature has not risen above 320 F. 
(160 C.) it is an indication that the acid was originally too 
weak or that too much gas was blown off. 1 If it is discovered 
during a cook that the usual method of relief will allow too 
much S0 2 to escape before the cook is done it may be remedied 
by closing the relief, drawing off some of the liquor from the 
bottom of the digester, and then again steaming. Some mills 
use this method regularly, relieving only to get rid of air and to 
reduce pressure before blowing. 2 

In practice the relieving of a digester is done from one or 
both of two points, either through the top or through the side. 
It is claimed by Wimmer 3 that side relief is a help in systematic 
cooking and also aids in the recovery of gas and the reduction 
of sulphur per ton of pulp. To use the side relief to the best 
advantage he recommends relieving from the top for about one 
and one-half to two hours, or until the temperature is 120 to 

1 Griffin and Little: Chemistry of Paper Making, p. 252. 

2 Steffanson: Paper, June 3, 19 14, p. 19. 

3 Wimmer: Paper, Jan. 19, 19 16, 15. 



190 THE SULPHITE PROCESS 

130 C. (248 to 266 F.), then, closing the top entirely, relieve 
from the side for one and one-half to two hours. After this top 
relief can be started again and only dry gas will ordinarily be 
obtained to the end of the cook. On large digesters there 
should be from three to five hours of dry gas. . 

As already stated the composition of the acid liquor varies 
greatly in different mills and with the nature of the fibre being 
made. Schlick x states that the strength of the pulp produced 
is in indirect proportion to the strength of the acid used. Ex- 
periments by the Forest Products Laboratory 2 appear to indi- 
cate that with a total SO2 content of 5 per cent, increasing the 
amount of combined SO2 above 1.0 per cent, has very little 
influence on the time of cooking while decreasing the combined 
acid below 1.0 per cent increases the speed of cooking. As the 
combined SO2 is decreased below 1 per cent there is an increase 
in the amount of screenings and in the bleach required. Other 
authorities place the lower limit for combined S0 2 at 0.75 per 
cent and agree that going below this point increases the bleach 
required. Decreasing the temperature of cooking between the 
limits of 146 C. and no° C. tended to increase the yield and 
decrease the screenings and the bleach required due to the more 
even cooking. Frohberg 3 claims that the rapidity of the diges- 
tion, other things being equal, is dependent solely on the con- 
centration of the free S0 2 and that in order to hasten the process 
dry wood and liquor rich in free S0 2 should be used. The 
present tendency is toward the use of acid of high strength, par- 
ticularly in free S0 2 . An increase in this factor enables the 
time of cooking and the final temperature to be reduced. The 
higher test for the digester acid means a higher blowing test at 
the end of the cook in order to obtain equal yields. It used to 
be stated that the best acid contained 75 per cent of its total 
S0 2 in the free state while now it is considered that 80 to 85 
per cent is a better figure. Much difference of opinion exists 

1 Schlick: Paper Pulp Mag. Can., 1915, 13, 227. 

2 Private communication. 

3 Wochbl. Papier-Fabr., 1910,41, 1179-1182. 



PROGRESS OF THE COOK 



191 



regarding the relative value of acids of different compositions 
and much more work will have to be done before the influence 
of all factors can be definitely established. 

In the cooking process irregularities are likely to occur from 
very obscure causes. Overcooking may be caused according to 
Klason : if too little lime is used. The minimum amount nec- 
essary to saturate the lignosulphonic acids is 22.5 grams per 
kilo of wood and if less than this amount is used the pulp is 
overcooked and charred. Overcooking may also result from 
decomposition of the liquor with formation of free sulphur 
according to the reaction 

3 S0 2 = 2 S0 3 + S. 

The sulphur acts catalytically, producing further decomposition 
of the calcium bisulphite, and the sulphuric acid combines with 
the lime as CaS0 4 so that not enough base is left to combine 
with the sulphonic acids which polymerize and eventually the 
fibre is attacked and darkened. Selenium in the cooking liquor 
will also act catalytically and with far greater power than free 
sulphur. Torgerson and Bay 2 have proved that it is not the 
selenium directly but the simultaneous presence of dust that 
causes the trouble. This dust acts as an energetic contact sub- 
stance promoting catalytic action of the selenium. This action 
is recognized by a sudden fall in the S0 2 and lime contents of 
the liquor after the digestion has proceeded for some time. 
The best way to determine the progress of a cook is to titrate 

portions of the liquor with — iodine solution which will show the 

10 

amount of total S0 2 . In taking samples from the digester for 
this test a cooler should be used, otherwise much of the S0 2 
will be lost. Another test which is frequently employed is to 
remove samples of the liquor and treat them with a mixture of 
strong ammonia and water in equal parts in test tubes. This 

1 Klason: Wochbl. Papier-Fabr., 19 10, 41, 464 et seq. 

2 Torgerson and Bay: Papier-Fabr., 1914, 12, 483. 



192 THE SULPHITE PROCESS 

causes the precipitation of calcium monosulphite which is at 
first light and voluminous but which decreases in quantity as 
the cooking proceeds. When a certain volume of precipitate 
is reached the cook is considered finished. This test is usually 
stated to show the amount of lime present as sulphite but 
according to Oman x it is virtually a test for S0 2 since if enough 
of the latter is present all of the lime will be precipitated. By 
taking the sample from the digester through a cooler and adding 
some calcium chloride to the ammonia used the test may be 
made to indicate the amount of SO2 present. The cooks in 
charge of the digesters also judge of the condition of the cook, 
to a certain extent, by the color and odor of samples of the 
liquor removed from the digester at frequent intervals toward 
the end of the cook. 

Recovery of Gas. The relief of gas and liquor from the 
digester during cooking causes a very large loss of sulphur 
dioxide and the recovery of this is an important item in keeping 
the cost for sulphur at a low point. This is accomplished by 
passing the relief through separators and coolers from which 
the gas is taken to the acid storage tanks where it is absorbed 
and brings the acid to the desired strength for cooking. The 
liquid portion from the separator is either allowed to go to 
waste or is mixed with the acid from the acid system previous 
to strengthening the latter with relieved gas. In Thome's 2 
recovery system the separated and cooled gas from the digester 
is passed into the bottom of a tower filled with wood blocks 
over which the acid from the acid system is passed, the strength- 
ened acid thus formed goes to the storage tanks. The liquor 
from the separator contains about 1 per cent of SO2 and after 
cooling it is sent to the acid system with the water or milk of 
lime as the case may be. This system is equally applicable 
to the limestone or milk of lime systems and by its use it is said 
to be possible to strengthen an acid of 2.60 per cent total and 
1 per cent combined S0 2 up to 5.50 per cent total with no in- 

1 Oman: Teknisk Tidskrift, 1916, 46, 4. 

2 Thome: Pulp Paper Mag. Can.., 1915, p. 173 (March 15). 



BLOWING AND WASHING 193 

crease in the amount of combined; moreover this is accomplished 
at a temperature of 35 C. (95 F.) with no loss of gas. 

In blowing down pressure before discharging the digester, the 
gas can be recovered by passing the gas and steam under the 
false bottom of a tower in which there is a continuous shower 
of water. This absorbs the gas and soon becomes heated by 
the steam to such a temperature that it can no longer hold the 
gas in solution. This liberated gas, together with that coming 
from the digester, soon increases to such an extent that the water 
supplied can no longer absorb it and there is delivered from the 
top of the tower a constant stream of pure gas which can be 
used in the acid system. 

In a few instances attempts have been made to recover the 
gas liberated when the digester is blown into the blow pits, but 
the volume of gas and steam which must be handled in a very 
short time is enormous and it is very doubtful if the results 
obtained pay for the expensive equipment and the cost of oper- 
ating. In one installation where this is being tried there has 
been no reduction in the amount of sulphur used per ton, indi- 
cating that the recovery is not a paying proposition. 

The sulphur consumption in practical work is generally fig- 
ured from the weight of sulphur fed to the burners and the 
tons of pulp produced. Bryant x states that in commercial 
work the sulphur consumption varies from 235 to 400 lbs. per 
ton and that the amount theoretically necessary, not taking 
the formation of sulphuric acid into account, would be 184 lbs. 
Schwalbe 2 gives the sulphur consumption as 9 to 10 kgs. per 
100 kgs. fibre (180 to 200 lbs. per 2000 lbs. fibre) and thinks that 
it should be possible to work with as little as 8 kgs. (160 lbs. per 
ton). Less sulphur per ton is used in the processes where in- 
direct steam is used because less loss is incurred by dilution and 
relieving liquor. 

Blowing and Washing. As already stated the contents of the 
digester are usually discharged into the blow pit under a pres- 

1 Bryant: Paper, Jan. 28, 19 14. 

2 Schwalbe: Chemie der Cellulose, p. 530. 



194 THE SULPHITE PROCESS 

sure of about 50 lbs. or less. The pipe from the digester to the 
blow pit may be of copper or even cast iron since the pitch in 
the pulp covers the inside of the pipe and prevents corrosion. 
This pipe is so arranged that the stock is discharged against a 
target placed in one end of the blow pit, to prevent wear on 
the pit walls. This target may be of bronze or of hard cast 
iron; the latter is generally used as it is cheaper, and offers 
more resistance to mechanical wear than bronze. As the acid 
at this stage is comparatively weak and the blowing is immedi- 
ately followed by washing the chemical resistance of the cast 
iron is sufficient for this purpose. 

Blow pits are of various shapes but consist essentially of 
tanks with false bottoms through which the waste liquor may 
drain. Modern American mills often use perforated tiles in the 
pit bottoms. They are frequently of reenforced concrete lined 
with wood of a resinous nature such as Southern pine or Doug- 
las fir. The washing is done by a stream of water from a 
hose, or by means of sprinkler pipes, and requires several hours. 
A novel wash pit arrangement is that proposed by Kuhn. 1 The 
entire floor is covered with drainer tiles and the wash water 
enters from below these tiles and is thoroughly mixed with the 
stock by air or steam forced through a series of perforated 
pipes laid on the surface of the tiles. After thorough mixing 
in this way the wash water is allowed to drain off by opening 
the appropriate valves. If desired this process can be repeated. 
The claim is made that the washing of 15 tons of dry fibre can 
be accomplished in 37 minutes as follows: 15 minutes for filling 
with hot water, 15 minutes for washing with air or steam and 
7 minutes for draining. 

The treatment of the pulp after washing is largely a mechani- 
cal one, to remove dirt, knots, slivers, and uncooked or partly 
cooked chips, by means of rifners, screens, etc. The screenings 
thus removed amount to 3 to 8 per cent of the pulp produced. 
During these mechanical purification processes the stock is very 

1 Kuhn: Papier-Fabr., 1915, 13, 725 and 744. 



ROSIN IN PULP 



195 



largely diluted; one authority gives the concentration of the 
stock as follows: 

In rifflers 250 parts water to 1 part pulp 

In coarse screens 125 parts water to 1 part pulp 

In fine screens 150 parts water to 1 part pulp 

The unbleached sulphite fibre found on the market shows 
wide variations in color, strength and physical properties. Its 
chemical composition also varies more or less as is proved by 
the following table. 

Analysis of Unbleached Spruce Sulphite Fibre * 

Per cent 

6-45 
0.65 

1-52 

81.51 

9-87 



Moisture, loss at 100 ° C 

Mineral matter (ash) 

Hydrocellulose, etc., soluble in alkali 

Cellulose 

Non-cellulose (lignin) by difference.. 



Per cent 


Per cent 


Per cent 


6. i S 


6.70 


6-57 


1 .00 


0.45 


o-33 


2-53 


2 .26 


4-25 


85-32 


89-74 


88 . 12 


5.00 


O.85 


o-73 



* Griffin and Little: Chemistry of Paper Making, p. 268. 

The ash in sulphite spruce fibre has been given considerable 
study by Richter. 1 He finds that it rarely exceeds 1 per cent 
and is usually about 0.5 per cent. Silica, generally amounting 
to about one-third of the total ash, is probably fixed as calcium 
or magnesium silicate during boiling as the silica present in the 
wood is too little to account for so much in the fibre ash. The 
percentage of iron in the ash showed no constant relationship to 
the total ash nor to any characteristics of the pulp. 

The rosin in sulphite has been given much attention because 
of its possible relation to rosin spots in the paper made from it. 
Herzberg gives the following percentages of rosin extracted by 
ether : 





Bleached 


Unbleached 


Mitscherlich pulp 


Per cent 

0.44 
o.43 


Per cent 
0.58 
°-59 


Ritter-Kellner pulp 





Other investigators find considerably higher amounts as 
follows : 

1 Richter: Wochbl. Papier- Fabr., 1913, 44, 1776. 



196 



THE SULPHITE PROCESS 



Ether soluble 



Alcohol soluble 



Total 



Foreign sulphites * . . 
American sulphites * 
Unbleached fibref. . 
Bleached fibre | 



Per cent 
0.70-1.33 
0.65-1 .21 
0.82-0.98 
o . 66-0 . q8 



Per cent 
0.10-0.22 
0.15-0.62 
0.18-0.82 
0.23-0.62 



Per cent 
0.90-1.43 
0.86-I .52 
1. 05-1. 67 
1 . 00-1 . 60 



* Richter: Wochbl. Papier-Fabr., 1913, 44, 4507. 
t Schwalbe: Wochbl. Papier-Fabr., 1913, 44, 3247. 

Both Richter 1 and Schwalbe 2 claim that the ether soluble 
portion is responsible for trouble with rosin spots. The total 
material contains both a fatty and a resinous constituent and 
Schwalbe has shown experimentally that neither constituent 
alone will produce rosin spots but that both together will give 
distinct and characteristic spots. The best means of avoiding 
rosin troubles seems to be seasoning the wood, which reduces 
the rosin soluble in ether and alcohol. Changes in the char- 
acter of the rosin extracted from the wood indicate that storage 
of chips for two to three weeks in the open air is as effective 
as storing the logs for two years. Richter 3 gives the following 
figures for rosin in cellulose from the same wood wet and dry. 





Rosin in cellulose 


Moisture in wood 


Ether soluble 


Alcohol soluble 


Total 


Per cent 

49 ° 
0.5 

35-o 
5° 


Per cent 
1 .00 
0.38 

I-3I 
0.88 


Per cent 

O.II 

0.26 
0.31 
0.36 


Per cent 
1 .11 
0.64 
1 .62 
1 .24 



Bleaching largely eliminates rosin troubles and with well- 
bleached pulp trouble from this source is seldom encountered. 

For the demonstration of rosin in sulphite fibre, Klemm 4 uses 
a strong solution of Sudan III in a mixture of three parts alcohol 

1 Richter: Wochbl. Papier-Fabr., 1913, 44, 2486. 

2 Schwalbe: Wochbl. Papier-Fabr., 1914, 45, 2926. 

3 Richter: Wochbl. Papier-Fabr., 1913, 44, 4621. 

4 Klemm: Wochbl. Papier-Fabr., 1911, 42, 967. 



MODIFIED SULPHITE PROCESSES * 197 

and one part water. The sample is reduced to a pulp with 
water, drained and the moist fibres treated with the dye. The 
excess is removed by blotting paper and the fibres mounted for 
observation in water. The rosin will be found stained orange 
red while the fibre is uncolored. 

Modified Sulphite Processes. Numerous modifications of 
the sulphite process have been tried out and patented from time 
to time. It would be impossible to enumerate all of these but 
a few may be mentioned as showing the trend of modern investi- 
gations. 

Eichmann 1 first subjects the wood to the action of gaseous 
SO2 and then boils with sulphite liquor as usual. 

Moore and Wolf 2 charge the digester with chips and liquor as 
usual, close the head and then inject gaseous S0 2 , air being 
allowed to escape. The charge is allowed to stand without heat- 
ing to allow the SO2 to penetrate and steam is then passed in 
until the cook is complete. The injection of S0 2 gas is 
repeated during the steaming to make up for the dilution by 
condensation. 

Morterud 3 takes the liquor from under a false bottom in the 
digester, passes it through a heater and back into the top of the 
digester, thus maintaining good circulation and cooking with 
weaker liquors because there is no subsequent dilution by con- 
densation. This process is giving excellent satisfaction in the 
sulphate pulp industry and is claimed to be equally applicable to 
the sulphite process. 

Sammet and Merrill 4 have obtained a United States patent for 
cooking with gaseous ammonia, sulphur dioxide and steam instead 
of the usual liquor. Somewhat similar is the process of Tyborow- 
ski 5 who causes ammonia to react with sulphite liquor, thus 
precipitating calcium monosulphite, which is removed, and 

1 German Patent 184,991, May 31, 1906. 

2 U. S. Patent 1,119,977, Dec. 8, 1914. 

3 German Patent: 286,074, Class 55b, Dec. 28, 1913. 

4 Paper Trade J., March 14, 191 2, p. 46. 

5 U. S. Patent 621,692, June 16, 1914. 



198 THE SULPHITE PROCESS 

obtaining a cooking liquor containing ammonium sulphite and 
free ammonia. 

The claims for nearly all of these modified processes are much 
alike, viz.: shorter time, lower temperature, lighter colored, 
stronger and easier bleaching fibre, greater yield, etc. 

By-products and Waste Liquor. The sulphite process offers 
opportunities for the recovery of by-products which are now lost 
during the period of relieving or in the waste liquor. Bergstrom * 
states that the vapors condensed from the digesters yield an 
aqueous distillate containing methyl alcohol, acetone, aldehyde 
and traces of acetic and formic acids together with a brown oil 
floating on the surface. This oil contains 7 per cent boiling 
between 150 and 160 C, 55 per cent boiling from 160 to 190 C. 
and 17 per cent boiling between 190 and 210 C. The portion 
boiling between 160 and 190 C. consists largely of cymene. 
The specific gravity of the various fractions varies from 0.845 to 
0.951. The same author 2 states that in the Ritter-Kellner 
process 8 to 10 kgs. of methyl alcohol are formed per ton of easy 
bleaching cellulose produced; of this about 3 kgs. may be obtained 
from the relieved gases. If the waste lyes are distilled in a 
continuous column apparatus the distillate contains methyl 
alcohol, acetaldehyde, acetone, oils and S0 2 as well as small 
quantities of formic and acetic acids. 

The problem presented by the waste liquors of the sulphite 
process is one which is not only interesting from a chemical 
standpoint but has also attracted much attention because of its 
bearing on stream pollution. In some cases, particularly in 
Europe, mills have even been obliged to close because it has been 
found impossible to purify the waste liquors sufficiently to com- 
ply with the legal requirements. While the industry in the 
United States is not confronted with quite such serious con- 
ditions it is only a question of time before much more complete 
purification will be demanded, so that the desirability of an early 

1 Bergstrom: Papier-Fabr., 1912, 10, 359. 

2 Bergstrom: Papier-Fabr., 1912, 10, 677. 



WASTE LIQUOR 



199 



solution is very evident. The present method of purification, if 
it may be called such, is merely to separate the fibres and neutral- 
ize the free acid with lime. The material thus removed is com- 
paratively small in amount considering that for every ton of 
fibre produced there is a ton of organic matter dissolved in the 
waste liquor. The total amount of this waste in the United 
States was estimated by the Geological Survey to be a billion 
pounds annually as long ago as 19 13. The discharge of such 
vast quantities of waste into streams renders the water injurious 
to health and makes it unfit for boiler use. It aids in the develop- 
ment of algae which may even grow in such quantities as to choke 
the streams. Under certain conditions it may cause the develop- 
ment of hydrogen sulphide with accompanying loss of oxygen in 
the water and consequent death of animal and vegetable life. 

Considerations of the nature outlined above as well as the 
desire to obtain useful and valuable products from a waste of 
such enormous magnitude have led many investigators to take 
hold of the problem. Walker x describes the waste liquor as a 
dark, reddish brown fluid of a specific gravity of about 1.05, and 
having a peculiar, not unpleasant odor. Among the constitu- 
ents present he mentions sulphur dioxide, sulphur trioxide, 
free sulphur, calcium and magnesium lignin sulphonates, pentoses 
and pentosans, mannose, dextrose, galactose, free furfural, traces 
of vanillin or vanillin-like body and small quantities of terpene- 
like substances. Waste liquors obtained in cooking hemlock 
wood have the following composition, according to Bryant : 2 





Grams per liter 


Pounds per ton of pulp 


Total solids 


115.00 

105.36 

9.64 

7-83 

0.76 


2999 

2748 

251 

204 

20 


Loss on ignition 


Ash 


Total sulphur 

Sulphur as SO3 



The specific gravity of this liquor was 1.0425. 



1 Walker: J. Soc. Chem. Ind., 32 (1913), 389. 

2 Bryant: Paper, 1914, Jan. 28. 



200 



THE SULPHITE PROCESSS 



Klason 1 calculates that for every ton (2202 lbs.) of dry fibre 
produced the waste liquor contains the following: 

600 kgs. (1320 lbs.) lignin. 

200 kgs. (441 lbs.) sulphur dioxide combined with lignin. 

90 kgs. (198 lbs.) CaO combined with lignin sulphonic acid. 
325 kgs. (717 lbs.) carbohydrates. 

15 kgs. (33 lbs.) proteins. 

30 kgs. (66 lbs.) rosin and fat. 

According to Krause 2 the principal constituent in the waste 
liquor is the calcium salt of lignin-sulphonic acid. Ritter-Kellner 
liquor is darker and contains more furfural and generally more 
sugars than Mitscherlich liquor. Wood boiled in the autumn 
contained about twice as much sugar as wood obtained in the 
spring. Very careful analyses of liquor from autumn cut wood 
gave the following figures: 





Mitscherlich process 


Ritter-Kellner 
process 


Furfural 


Per cent 

O.OI 

0.40 
0.21 
1.48 
0.47 
0.48 
0.28 

O.OI 


Per cent 
0.02 


Pentosans 


0.29 
0.49 

1-47 
0.41 
0.48 


Hexosans 


Total sugars 


Pentoses 


Mannose 


Levulose 


0.25 

O.OI 


Galactose 


Dextrose 


Trace 







According to Johnsen 3 the volume of liquor which can be 
obtained without special apparatus is 740 to 800 gallons per ton of 
pulp, while Haegglund 4 claims to obtain 960 gallons. Great 
differences of opinion also exist as to the rate of formation of 
fermentable sugar during the cook. Krieble 5 states that most of 
the sugar is formed before the end of the seventh hour and that 

1 Klason: Papier-Fabr., 1909, 26, 627, 671, 703. 

2 Krause: Chem. Ind., 1906, 29, 217. 

3 Johnsen: Pulp Paper Mag. Can., 16, 1918, 314. 

4 Haegglund: Pulp Paper Mag. Can., 15, 1917, 1185. 

5 Krieble: Paper, 23, 1919, 753. 



WASTE LIQUOR 2 OI 

part of the fermentable material is destroyed if the temperature 
rises above 145 C. after that time. Haegglund, on the other 
hand, claims that only a little sugar is formed during the first six 
or eight hours but that it increases rapidly on longer cooking, 
the rate depending on temperature and composition of the cooking 
acid. 

Hoenig * claims that no organic acids except formic and acetic 
are present and that the ratio of these is 1 : 1.56. He finds 2.15 
to 9.08 grams of volatile acid per liter. 

The waste liquor, according to Walker, 2 yields brominated and 
chlorinated products; it contains active carbonyl and methyl 
groups and is a strong reducing agent. On addition of alcohol 
the chief constituents are precipitated as a dark, gummy mass 
which becomes brittle on drying. This may also be obtained by 
salting out with sodium chloride or by treating with concentrated 
mineral acids or lead acetate. It is almost impossible to purify 
this substance because of its colloidal nature and its limited 
solubility in the usual organic solvents. 

The attempts to utilize the materials in this waste liquor have 
been very numerous and many patents have been issued covering 
all kinds of industries. A complete enumeration of all the 
patents in detail would occupy too much space and moreover it 
has been well covered by Miiller 3 up to the year 191 1 and also 
by Johnsen and Hovey. 4 A brief outline of the more important 
uses, or proposed uses, is therefore all that will be attempted here. 
As a binder the waste liquor, either in its original strength or 
concentrated by evaporation, has been tried for various purposes. 
As a road binder liquor at 1.13 sp. gr. has given very fair service 
when sprinkled upon the streets. While it is not water-resistant, 
the roads to which it has been applied appear to resist the action 
of rains fully as well as those to which crude oil has been applied. 
This use has only local interest because of the cost of transporting 

1 Hoenig: Chem. Ztg., 19 12, 36, 889. 

2 Walker: J. Soc. Chem. Ind., 32 (1913), 389. 

3 Miiller: Literatur der Sulfit-Ablauge. 

4 Bulletin 66, Dept. of Interior, Canada, 1919. 



202 



THE SULPHITE PROCESS 



the relatively dilute liquors. In preparing briquettes from 
waste coal it has met with some success, the briquettes being 
hard and making excellent fuel in ordinary grates or in smelting 
furnaces. An advantage which it possesses for this work is that 
the briquettes do not soften on heating and hence hold their 
shape well in use. On the other hand, the high percentages of 
ash and sulphur are detrimental in some cases. The briquetting 
of pyrites, wood waste, iron ores and other materials has also 
been successfully carried out by means of the concentrated waste 
liquor. Another use as a binder is in the iron foundry where 
it is mixed with the sand in preparing the moulds. Stutzer 1 
gives the following as the composition of a sulphite waste liquor 
and two concentrated products made therefrom: 





Original waste 
liquor 


Wood extract 


Cell pitch 


Dry matter 

Ash constituents 


I2.l8 
I.44 
O.87 
O.85 
O.24 . 


63.88 
2 64 
0.50 
4.80 

o.iS 


82.79 
14.90 


Lime 

Total sulphur 

S0 2 


8.50 
5 87 
0.85 



In the preparation of concentrated products either iron or 
copper apparatus may be used, but if the former is employed the 
acid in the liquor must be neutralized by lime. Direct evapora- 
tion in copper is preferable if the product is to be used in tanning. 
A multiple effect evaporator is generally employed to bring the 
liquor to 35 Be. and the final concentration is performed on 
drums one of which will bring it up to 6o° Be. while a second will 
convert it to a solid. The pitch appears as a black opaque resin 
but is soluble in water. About 1 kg. of dry pitch is obtained 
from 10 kgs. of waste liquor and for each ton produced about a 
ton of coal is required. 

It has been proposed by Knosel 2 to prepare a fertilizer from 
the waste liquor by evaporating to about 25 Be. and mixing with 

1 Stutzer: Papier Ztg., 1911, 36, 5. 

2 Knosel: German Pat. 128,213. 



USES FOR WASTE LIQUOR 203 

about an equal weight of ground Thomas slag. Analyses of this 
product show that practically all the phosphoric acid is in the 
citrate' soluble form. 

The use of sulphite waste liquor in the sizing of paper has been 
proposed by Mitscherlich 1 who mixed the liquor with gelatin 
solution and separated the precipitate formed. This was then 
dissolved in weak alkali and added to the paper stock in which 
it was precipitated by alum. A sizing process of another kind 
is that of Klason 2 in which the waste liquor is used instead of 
alum as a precipitant for silicate of soda. Neither of these 
processes has ever come into extensive use. 

Stutzer 3 has investigated the possibilities of waste liquor in 
the preparation of cattle feed and asserts that in each kilo, con- 
taining 120 grams per liter of solids, there are 550 calories which 
can be made available by feeding. His proposed treatment is to 
evaporate 100 liters to 50 liters in a vacuum, mix with 0.5 kg. 
of formaldehyde and ground limestone and then filter. The 
filtrate, after further evaporation, is mixed with molasses and 
6.25 kgs. of peat to give 45 kgs. of cattle food. 

In the dyestuff industry it has been used as the basis for the 
manufacture of sulphur dyes, in the reduction of indigo and in 
the preparation of indanthrene and similar dyes. The sodium 
Hgnin sulphonate prepared from it has been employed to replace 
tartaric acid in mordanting wool. 

Strehlenert 4 has proposed the following method for the prepa- 
ration of lignin and the recovery of sulphur dioxide. A little 
acid sodium sulphate is added to the fresh hot liquor and the 
calcium sulphate which precipitates is separated. The hot liquor 
is then run into digesters and heated to ioo° C. ; air is pumped in 
until the pressure reaches 18 atmospheres, when the temper- 
ature rises 20 because of the chemical reactions taking place. 
Heating is continued to 160 C. Between 160 and 170 C. is 

1 Mitscherlich: German Pat. 54,206, 1890. 
. 2 Klason: Z. angew. Chem., 22 (1909), 1423. 

3 Stutzer: Z. angew. Chem., 22 (1909), 1999. 

4 Strehlenert: Papier-Fabr., 1913, II, 645, 666. 



204 THE SULPHITE PROCESS 

the critical point at which decomposition of the lignin sulphonic 
acid begins. This reaction causes the temperature to rise about 
2o° more and it is finally forced up to 200 C. The time after 
reaching ioo° C. is about 40 to 60 minutes. If properly con- 
ducted this procedure causes the evolution of sulphur dioxide, 
which can be recovered, while the lignin is precipitated in 
granular form and can be used as fuel after partial drying. The 
sulphur recovery is claimed to be 25 to 30 kgs. (55 to 66 lbs.) per 
ton of pulp and the lignin enough to supply the entire fuel 
requirements of the pulp mill. 

The use of the dried waste liquor as a fuel is suggested be- 
cause of the large amount of combustible matter which it con- 
tains. The dry material is light, powdery and has a heating 
value of about 6000 B.t.u. per pound. ■ Experiments in burn- 
ing this in the same manner as powdered coal 1 gave excellent 
results and the ash formed in easily accessible places and showed 
no tendency to fuse. 

Rinman 2 mixes the waste liquor with lime to make 22 to 25 
grams per liter of calcium oxide and boils first for five hours at a 
low temperature and finally at 180 C. The precipitate of cal- 
cium sulphite and humus is filtered off and treated with sulphur 
dioxide to recover the calcium bisulphite. The alkaline filtrate 
is evaporated to 40 Be., more lime is added, the mass evapo- 
rated to dryness and finally destructively distilled in presence 
of steam. The products of this latter process include acetone 
and low and high boiling oils. 

The preparation of a material for use in making insulating 
substances or artificial leather is patented by Trainer. 3 The 
waste liquor is evaporated to 30 Be. and then heated with an 
acid, preferably after adding an aldehyde such as formaldehyde. 

Extracts for use in tanning leather are prepared in consider- 
able quantities by processes involving neutralization with lime, 
concentration, and subsequent separation of the organic and 

1 Paper, Dec. 19, 1917. 

2 Papier Ztg., Apr. 4, 1915. 

3 Trainer: German Pat. 197,195, Feb. 20, 1906. . 



USES FOR WASTE LIQUOR 205 

inorganic materials. The extracts obtained contain practically 
no true tannins but do contain materials which are taken up by 
the skins and act as fillers. While these extracts are not suit- 
able for tanning alone they find a legitimate use as additions 
to other true tanning substances. 

The preparation of alcohol l from waste lyes has probably 
attracted more attention than any other method of utilization 
and a number of commercial plants are already in successful 
operation. The two principal processes now in use are the 
Swedish, which is a combination of the Wallin and Ekstrom proc- 
esses, and the Norwegian or Landmark method. The principle 
of all processes is the fermentation of the sugars present followed 
by the distillation of the alcohol formed, and one of the prin- 
cipal difficulties encountered has been due to the poisoning of 
the yeast by traces of sulphur dioxide. The Swedish process 
uses a tempered yeast which is capable of resisting this action. 
The liquor is first neutralized by calcium carbonate arid the 
last traces of acidity by calcium hydroxide, it is then cooled, 
settled and run to the fermentation vats where the yeast is 
added. It is fermented at 27 C. for four or five days and then 
distilled. The raw alcohol contains 92 to 93 per cent of ethyl 
alcohol, 3 to 4 per cent methyl alcohol and small amounts of 
cymol, acetone and aldehyde. The yield of 100 per cent alcohol 
by this process is said to be 74 liters per ton of dry sulphite, 
and the cost about 12 cents per U. S. gallon 180 proof. 

In the Norwegian process the fermentation is aided by a 
nutrient and easily fermentable medium prepared from milk 
or whey. To the milk an equal volume of sulphite liquor is 
added and a small amount of muriatic acid and the precipitated 
ligno-casein filtered off. The filtrate is then added to the waste 
liquor and the mixture evaporated to a concentration of about 
15 per cent. It is next neutralized by powdered limestone, 
cooled to 2 7 C. and the yeast added; in this case ordinary 

1 Tartar: J. Ind. and Eng. Chem., 1916, 226; Hedalen: Pulp Paper Mag. 
Can., 1916, 176; Kiby: Chem. Ztg., 1915, 39, 212 et seq.; Segerfelt: Papier. Ztg., 
53, 2518, 2558. 



206 THE SULPHITE PROCESS 

brewers' yeast has proved entirely satisfactory. After four or 
five days' fermentation it is ready to be distilled. The yield by 
this process is claimed to be 91.2 liters of 100 per cent alcohol 
per ton of dry sulphite, and the cost about 9 cents per U. S. 
gallon 180 proof. 

According to McKee l the so-called poisoning of the yeast 
is not due to sulphur dioxide but to the lack of oxygen. He 
has patented a process in which the hot waste liquor is cooled 
by blowing air through it and then placed in closed fermenta- 
tion tanks where it is kept Agitated during the fermentation 
period by a slow current of air. Under these conditions fer- 
mentation proceeds satisfactorily with ordinary yeast even in 
the presence of very considerable amounts of sulphur dioxide. 
Loss of alcohol is prevented by scrubbing the exit gases from 
the fermentation tanks with unfermented liquor. 

According to Stalnacke 2 three mills in Sweden were produc- 
ing in 1916 about 660,000 gals, of 100 per cent alcohol annually, 
while the total possible production was about 6,868,000 gals. 
Considering the equipment necessary he states that for a mill 
making 55 tons of cellulose the fermentation vats should hold 
264,000 gals, and the distilling apparatus should be capable of 
handling about 2400 gals, per hour. 

While the preparation of alcohol from the waste liquor is a 
profitable undertaking it does not solve the problem of the dis- 
posal of the liquor since the spent fermentation residues are 
nearly as objectionable as the original waste. 

Other substances which it has been proposed to recover from 
the waste liquor are antiseptic materials, calcium sulphite, cal- 
cium sulphate, coniferin, cymol, acetic acid, furfural, levulinic 
acid, oxalic acid, sulphur, turpentine, lignorosin, vanillin, etc. 
Many of these can be obtained only in small amounts and the 
demand and the prices obtainable are not such as to make the 
undertaking attractive. 

1 McKee: Paper Trade J., 1918, Aug. 22, p. 42. 

2 Stalnacke: Paper, Apr. 5, 1916. 



TESTS AND ANALYSES 207 

While much progress has been made there is still a tremen- 
dous amount of work to be done before the utilization of this 
enormous amount of waste can be considered satisfactory. The 
quantity of material to be handled would seem to indicate that 
such investigations should be directed towards the production 
of large amounts of products at small profits rather than the 
preparation of small quantities of substances of relatively high 
value per pound. 

Tests and Analyses for the Sulphite Process — Sulphur. 
Sulphur as obtained at present on the American market is of a 
very high degree of purity but it is nevertheless well to examine 
it occasionally. 

Moisture may be determined by weighing a 3 to 5 gram por- 
tion into a weighing bottle, drying to constant weight at 70 to 
8o° C, cooling and again weighing. The heating should not 
be prolonged beyond the time necessary to reach constant 
weight and the temperature must not be allowed to rise too 
high. 

To determine non- volatile substances a 10 gram sample is 
cautiously heated in a porcelain crucible on a sand bath until 
nearly all of the sulphur has volatilized (ignition of the sulphur 
must not take place). Cover the crucible with a perforated 
lid and pass into it pure, dry hydrogen gas until all sulphur 
has escaped; cool and weigh as non- volatile matter. 

The inorganic ash may be determined by igniting the non- 
volatile matter with access of air and reweighing after cooling. 

Selenium may be determined according to the method of 
W. Smith 1 as follows: Weigh 30 to 50 grams of the finely 
ground sulphur into an Erlenmeyer flask, add a few cubic centi- 
meters more bromine than the grams of sulphur used and allow 
it to stand 15 minutes. Transfer to a 100 c.c. separatory funnel 
and shake vigorously with 40 c.c. of bromine water for one 
minute. Separate the sulphur bromide from the aqueous solu- 
tion and pour the latter through a wetted filter paper. Add 

1 W. Smith: J. Ind. Eng. Chem., 1915, 7, 849. 



208 THE SULPHITE PROCESS 

about 2 c.c. of bromine and 40 c.c. of bromine water to the 
sulphur bromide, and repeat the extraction four times, keeping 
the last extract separate. Treat the last extract in the same 
way as the combined extracts, using proportionate parts of 
potassium iodide and hydrochloric acid and if the presence of 
selenium is proved repeat the extraction as often as necessary. 
The combined extracts are boiled till clear and any remaining 
free bromine is removed by careful additions of powdered 
potassium metabisulphite or sulphite until the solution just 
becomes colorless. Dilute to about 250 c.c, add 15 c.c. of 
hydrochloric acid and about 5 grams of potassium iodide and 
boil; this completes the precipitation of the selenium, and 
gradually converts the red to the black form. The free iodine 
is removed by a few cubic centimeters of potassium sulphite 
solution; the solution is boiled for 20 minutes, filtered through 
a tared Gooch crucible, the selenium washed with hot water, 
and dried at ioo° C. until constant in weight. 

Burner Gases. In order to control the burners properly the 
gases should be tested once an hour, or oftener if the burners 
are not working satisfactorily. The sulphur dioxide may be 
determined by means of an Orsat apparatus using caustic soda 
in the absorption pipette. The gas is measured in the burette 
over water which soon becomes saturated with S0 2 and then 
introduces only a very slight error. 

Excess air may be estimated by determining the oxygen by 
means of alkaline pyrogallate after first absorbing the SO2 in 
caustic soda. This test gives valuable information regarding 
leaks in the apparatus between the combustion chamber and 
the absorption system. 

Sulphur trioxide in the gases is very difficult to determine 
with accuracy. Richter 1 passes the gas, at a rate of 1000 c.c. 
in 20 to 25 minutes, first through a hard glass sampling tube 
surrounded with an iron jacket and then through a tube 30 cms. 
long which is filled with garnets and bits of porcelain and cooled 

1 Papier-Fabr., 11, 1913, p. 610. 



TESTS AND ANALYSIS 209 

with ice. The gas is measured by the amount of water de- 
livered by the syphon bottle which is used to induce its flow. 
After passing 2 to 5 liters of gas the tube is washed out by 
drawing pure air through it and finally is washed into a beaker 
with water to remove the S0 3 . This is then determined gravi- 
metrically by precipitation as BaSCV 

The generally accepted place to sample the gases is in the 
main pipe between the cooler and the absorption apparatus. 

Besides these chemical tests it is customary to record the 
temperature of the gases as they leave the combustion chamber 
and again after passing the cooler. Some form of recording 
pyrometer is desirable for the former work while an ordinary 
chemical thermometer is satisfactory for the latter. 

"Acid" or Bisulphite Liquor. Samples of the liquor delivered 
by the absorption apparatus are generally tested once an hour 
and the liquor in the storage tanks whenever a digester is filled. 

For total S0 2 a 1 c.c. sample is taken by means of a pipette 

and diluted with 200 to 300 c.c. of water in a white porcelain 

N 
bowl. A few drops of starch solution are added and then — 

10 

iodine solution is run in until a blue color appears. 

N 
For free, or available, S0 2 a 1 c.c. sample is titrated with — 

10 

caustic soda, using phenolphthalein as an indicator. 

The combined S0 2 is the difference between the total and 
free S0 2 . 

The tests given are those generally made by the mill foremen 
and are intended to give comparative rather than absolute 
results. They are subject to errors because of the small size of 
the sample, and because the pipette is not usually washed out 
and hence a little of the liquor always remains adhering to the 
glass. It is customary to read from a chart the amount of 
either free or total S0 2 corresponding to the volume of caustic 
soda or iodine used. This is generally spoken of as per cent, but 
it is not exactly that as the test made in this way takes no 
account of the specific gravity of the liquor. 



2IO THE SULPHITE PROCESS 

For accurate analyses of the liquor a sample of 10 c.c. should 
be diluted with recently boiled and cooled water to ioo c.c. and 
10 c.c. of this used in the tests. 

Sulphates in the liquor may be determined by placing 10 c.c. 
in a covered beaker, adding an excess of strong hydrochloric 
acid and boiling for some time until the odor of S0 2 is no longer 
noticeable. The sample is then diluted and the S0 3 determined 
gravimetrically as BaS0 4 . 

Bases may be determined by the following method given by 
Griffin and Little. 1 Ten to twenty cubic centimeters of the 
acid are treated with H 2 S0 4 in slight excess in a platinum dish, 
and evaporated to dryness. The dry mass is cautiously ignited 
until no more fumes come off, and the residue cooled and weighed 
as sulphates of calcium and magnesium. 

Treat the sulphates with 5 c.c. of water and one or two drops 
of hydrochloric acid and break up all lumps with a stirring rod. 
Rinse into a beaker with as little water as possible, add one or 
two drops of strong sulphuric acid and alcohol equivalent to 
twice the volume in the beaker. Allow it to stand with occa- 
sional stirring for an hour or more, then filter off and wash the 
precipitate first two or three times with 60 per cent alcohol 
and finally with 40 per cent alcohol as long as anything is removed 
by the treatment. The residue on the filter is dried, ignited, 
and weighed as pure calcium sulphate. 

Selenium. As a practical test for the presence of selenium 
in injurious quantities, Klason and Mellquist 2 seal up some of 
the liquor in glass tubes, from which air has been expelled by 
carbon dioxide, and heat for 15 hours at 13 7 C. in a bath 
of boiling xylene. If appreciable amounts of selenium are pres- 
ent, the composition of the liquor will be changed by this 
procedure. 

Waste Liquor. At the end of the cook the liquor in the 

N 
digester is tested for total S0 2 by means of — iodine. The 

10 

1 Chemistry of Paper Making, p. 414. 

2 Klason and Mellquist: Papier-Fabr., 19 13, 145. 



TESTS AND ANALYSIS 211 

sample is generally drawn from about one-third the way down 
the digester and no attempt is made to retain the S0 2 by cooling 
the liquor as drawn. Of this hot liquor a 5 c.c. sample is gen- 
erally tested. 

For the determination of free S0 2 in waste liquor, Stutzer 1 
recommends the following: Place 25 c.c. of the liquor in an 
Erlenmeyer flask, add 25 c.c. of standard alkali, then 1 gram of 
ammonium chloride or nitrate and immediately connect with a 
condenser. Boil for just 20 minutes and catch condensate in 
25 c.c. of standard acid. The acid not neutralized by this treat- 
ment is equivalent to the free acid in the waste liquor. 

1 Stutzer: Papier Ztg., 1911, 36, 5. 



CHAPTER VII 
GROUND WOOD OR MECHANICAL PULP 

The preparation of ground wood pulp brings in comparatively 
little of a chemical nature yet its close relationship to the rest 
of the industry makes it desirable to include a discussion of the 
methods and general principles involved. The commercial man- 
ufacture of ground wood is generally not conducted according 
to any fixed standards of practice, each superintendent or man- 
ager having his own theories about the best methods of operating. 
For this reason little reliable information was available until 
the Forest Service undertook the collection of data and it is 
upon their results x that much of the present chapter is based. 

The present method of manufacture has been in use for a 
long time and except for increased size and capacity of grinders 
it has changed but little since its introduction in 1867. The 
process consists briefly in pressing blocks of wood against the 
surface of a grindstone which is also supplied with water to 
remove the pulp as fast as it is made. The stones are usually 
about 54 ins. in diameter by 27 ins. face, but in some recent 
installations have been as large as 60 ins. in diameter by 48 ins. 
face. Up to a few years ago natural quarried stones only were 
used, but many mills are now experimenting with artificial stones. 
The wood to be ground is placed in pockets in the housing of 
the stone in such a way that the logs are parallel with the shaft 
on which the stone is mounted. Pistons operated by hydraulic 
pressure then force the wood against the stone until it is reduced 
to pulp. The pockets are tjien recharged and the process re- 

1 Forest Service Bulletin, Experiments with Jack Pine and Hemlock. Forest 
Service Bulletin 127, Grinding Spruce for Mechanical Pulp. Forest Service Bulle- 
tin 343, Ground-Wood Pulp. 

212 



GROUND WOOD OR MECHANICAL PULP 



213 



peated. There are generally three or four pockets for each 
grinder and as they seldom become empty all at once they are 
filled as necessary and the process is thus continuous. 

There is now on the market a magazine grinder equipped 
with two pockets into which the wood is fed automatically. 
The Voith Magazine Grinder, shown in part sectional elevation 




Fig. 31. Three-pocket Grinder 
(1) Grindstone (2) Shaft (3) Steel flanges (4) Casings or side frames 
(5) Bridge-trees (6) Studs to support (7) Pockets (8) Hydraulic cylin- 
ders (9) Piston rods (10) Pressure foot 

in Fig- 33 is of this type. The advantages of this grinder are 
said to be (1) increased capacity, (2) charging is automatic and 
not subject to the irregularities of manual feeding, (3) constant 
load on motor or turbine and (4) decreased cost of attendance. 
The pulp coming away from the stones collects in pits under 
the grinders and from these pits it flows to screens with one- 
fourth to three-fourths inch perforations which remove slabs, 
knots, large splinters, etc. For satisfactory operation of these 



214 



GROUND WOOD OR MECHANICAL PULP 



screens the stock should be diluted to at least i per cent dry 
matter. The stock passing these coarse screens goes next to 
the regular screens of centrifugal or diaphragm type, and for 
this operation it should be still further diluted to about 0.25 




Fig. 32. Three-pocket Grinder Sectional Elevation 

per cent dry. It is desirable that the diluted stock be passed 
through a riffler or over a sand settler before going to the screens 
as much wear on the latter is thus avoided. The screened 
stock is then thickened to the proper consistency for use in the 
beaters by means of filters, wet machines, or some other equiva- 



GROUND WOOD OR MECHANICAL PULP 



215 



lent device, or if it is to be sold in the form of "laps" these are 
made on a wet press. 

The chief factors which enter into the production of mechani- 
cal pulp from any species of wood are: 

(1) Surface of stone; whether rough or smooth, sharp or dull, 
or of coarse or fine grit. 



Suspension IJin for swinging 
magazine out to narg stone 



Charging Floor 




-" L C ' ' "<?tSJ >c , \-a~- J 



Fig. 33. Voith Magazine Grinder 

(2) Pressure employed in forcing the wood against the re- 
volving stone. 

(3) Peripheral speed of the stone. 

(4) Temperature of grinding and thickness of stock in the 
grinder pit. 

(5) Physical condition of the wood. 



216 GROUND WOOD OR MECHANICAL PULP 

The condition of the surface of the stone depends on several 
factors among them being the size and sharpness of the indi- 
vidual particles of grit, the ease with which the binding mate- 
rial wears away and the manner of dressing the stone. This 
latter operation is performed by working across the face of the 
stone small steel rolls or burrs of various designs which roughen 
the surface and form depressions through which the ground 
wood can escape. A great deal of attention has been given to 
the designing of these burrs but it appears that practically the 
same quality of pulp can be obtained under like conditions of 
pressure, speed and temperature if the surface is brought to 
the same condition of sharpness of grit, regardless of whether 
the design of the markings is straight cut, spiral or diamond 
point. The important thing, so far as quality is concerned, is 
to give the particles of grit the correct treatment, rather than 
to form a deeply grooved surface. 

The horsepower per ton of pulp varies inversely with the 
sharpness of the stone, while the production varies directly 
with the sharpness. Immediately after sharpening a stone, 
therefore, the rate of production is high and the power con- 
sumed low, while as the stone becomes dull the former de- 
creases and the latter increases. The condition of the surface 
of the stone appears to have very little influence upon the 
yield per cord unless it has been made so extremely sharp that 
more screenings are formed and possibly more fine fibre lost in 
the white water. With such a surface the fibres are actually 
ground to pieces and in some instances they are so short and 
fine that it is almost impossible to remove the lap from the 
wet machine press rolL Deep grooving of the surface of the 
stone causes more rapid production of pulp but at the expense 
of quality, while better pulp is produced by a less sharp stone 
and a greater application of power. Paper prepared from this 
latter pulp has greater strength than that from pulp ground 
on very sharp stones. 

Next to the surface condition of the stone the factor most 
influencing quality is the pressure at which the wood is forced 



GROUND WOOD OR MECHANICAL PULP 217 

against the stone. For any given cylinder pressure this varies 
greatly with the length and diameter of the logs, and further 
variations are caused by the binding of the wood in the pockets 
and by fluctuations in the water pressure when the pistons are 
raised or lowered. The result of increasing the pressure is to 
increase the power required by the grinder and decrease the 
power consumption per ton of pulp made. This latter effect 
is less noticeable on sharp than on dull stones. This result 
is interesting because it suggests that by carrying a high 
pressure and using only part of the pockets the power con- 
sumption per ton can be reduced, or in other words these con- 
ditions permit the production of a larger quantity of pulp during 
times of low water, without sharpening the stone to an unusual 
degree. 

It has been found that the yield of pulp per 100 cu. ft. of solid 
wood increases with increase of pressure. The screenings also 
increase, but not so fast as the total yield so that there is a net 
gain of good fibre. The strength factor, or the bursting strength 
per square inch divided by the weight per ream, which indicates 
the quality of the pulp, decreases quite rapidly with increasing 
pressure. 

The peripheral speed of the stone is given little attention in 
most commercial plants. When the pressure on a pocket of the 
grinder is removed the speed increases greatly, which counteracts 
to a certain extent the decreased production due to the smaller 
number of pockets in use. While this is rather beneficial than 
otherwise there are conditions of operation which require a fairly 
constant speed, and the use of a governor is therefore desirable. 
As would be expected the power to the grinder varies directly 
with the speed; this is also true, and to an even greater extent, 
of the production in twenty-four hours. With constant power 
to the grinder the production in twenty-four hours is practically 
constant, regardless of whether the pulp is produced at low 
pressure and high speed or at high pressure and low speed. The 
strength of the paper is greater with pulp produced at high pres- 
sure and low speed than with that made at low pressure and high 



218 GROUND WOOD OR MECHANICAL PULP 

speed. The yield per cord and the quality of the pulp are only 
slightly influenced by the speed. 

The effect of the temperature at which mechanical pulp is 
produced has long been a controversial point between European 
and American manufacturers. The general American practice 
is to operate at high temperature and it is claimed that pulp so 
produced has longer and stronger fibres, is considerably tougher 
than cold-ground pulp and works "freer" on the paper machine. 
Cold-ground pulp, on the other hand, is said to be finer, more 
free from shives and to give a better closed sheet of greater 
opacity than hot ground pulp. 

Another factor which is claimed to have an important influence 
on the paper produced is the thickness of the pulp in the grinder 
pit, and in actual operations this varies from extremely thick to 
comparatively thin. 

Investigation of these two points shows that varying the tem- 
perature from hot to cold has little effect upon the power con- 
sumption or power to grinder, but the production in twenty-four 
hours is somewhat higher when grinding hot. With thick stock 
in the grinder pit the power required to rotate the grinder with- 
out load is greater than with thin stock, but the difference, when 
calculated to the basis of power consumption per ton of pulp, 
becomes negligible. Neither of these two factors of temperature 
and thickness of stock influences the yield per cord of wood. The 
quality of pulp, however, is affected, that produced at high tem- 
perature being long-fibred, while a fine-fibred stock is more 
easily secured by the cold grinding process. 

The physical condition of the wood, apart from any changes 
induced by boiling or steaming, has a very appreciable influence 
on the results obtained. For green wood the average power con- 
sumption is lower than for seasoned wood while the rate of pro- 
duction is higher. The diameter of the bolts used and the rate 
of growth of the wood have very little effect upon either the 
power consumption or the rate of production. Rapidly grown 
wood, as compared with that which has grown slowly, yields 
considerably less pulp which is softer though of about the same 



GROUND WOOD OR MECHANICAL PULP 219 

strength as that from slowly grown trees. It is generally recog- 
nized that green or freshly cut wood gives a better product than 
seasoned wood, and in the case of white fir McNaughton 1 has 
shown that pulp from young trees 18 ins. or less in diameter is 
whiter and stronger than that from old trees of about 40 ins. 
diameter. 

The commercial efficiency in converting rossed wood to pulp 
under ordinary conditions averages about 88 per cent. Of the 
remaining 12 per cent about 2 to 7 per cent is lost as screenings 
and in the white water as wood fibre, while the remaining 5 to 
10 per cent must be in the white water as water soluble organic 
or inorganic materials. 

The changes induced by boiling or steaming the wood before 
grinding very profoundly influence the product obtained. The 
color of the pulp is darker than that from unsteamed wood and 
the fibres are much longer and better separated, resulting in a 
stronger product. The changes in color and physical character 
of the pulp are practically identical, provided the temperature 
and duration of the cooking are the same, whether the logs are 
steamed or boiled while immersed in water. Steaming has the 
advantage over boiling in that less heat is necessary and the con- 
densed liquors are drawn off in concentrated form which is a ben- 
efit where recovery of by-products is attempted. As soon. as 
steaming starts the formation of acid commences and increases 
up to the end of eight hours treatment. Both acetic and formic 
acids are produced, in the ratio of six acetic to one formic. Spruce 
gives 0.213 per cent of acetic acid and pine yields similar amounts. 
After two hours steaming reducing sugars appear and eventually 
amount to about 0.25 per cent of the dry wood. 

The pressure and duration of steaming are important factors 
to control since they have a great influence on the color, strength 
and yield of pulp. Increasing both time and steam pressure 
increases the strength of the pulp but makes it much darker in 
color while at the same time the yield is much decreased because 
of the greater solvent power of the water. 

1 Paper, Nov. 1, 1916, p. 13. 



220 GROUND WOOD OR MECHANICAL PULP 

A study of the various factors in the grinding of steamed spruce 
wood has brought out a number of very interesting facts. The 
power required per ton of pulp is at least 25 per cent greater than 
that used in grinding untreated wood, and the maximum power 
per ton is reached when the wood is cooked for six hours. This 
holds true for cooking pressures between o and 75 lbs. gauge pres- 
sure. With the same length of cooking, wood which is treated 
at high pressure requires more power per ton of pulp than that 
which has been cooked at lower pressures, while with a fixed 
amount of power to the grinder the amount of pulp produced is 
less at high pressure and low speed than it is at low pressure and 
high speed. 

The pulp made by grinding steamed wood can be used for 
different purposes, depending on the nature of the grinding 
process. If a sharp and coarse stone is used a large number of 
shives will be present and the pulp will serve for the manufacture 
of box boards or similar products. When ground to a finer state, 
and mixed with a small amount of chemical fibre a bogus kraft 
paper can be produced which will serve for a cheap wrapping 
paper. Tests on papers made from steamed and unsteamed 
woods show that the steamed pulps give a higher percentage of 
stretch than the unsteamed even though the latter are mixed 
with 20 per cent of sulphite spruce fibre. Like chemical pulps 
steamed ground wood is considerably influenced by beating 
treatments and variations in the latter cause marked variations 
in the strength of the paper. With prolonged beating the paper 
becomes more brittle but gives higher strength tests. 

The boiling or steaming of wood results in the formation of a 
natural size from some of its constitutents and this sizing action 
is particularly noticeable in the production of pulps from the 
hardwoods — birch and aspen — which are not naturally pitchy. 
All paper produced from cooked woods, pulped by the mechanical 
process, shows the characteristic water-resistant qualities and 
hardness of hard sized papers. 

While spruce is the standard wood for the manufacture of 
mechanical pulp the supply of this wood is decreasing so rapidly 



GROUND WOOD OR MECHANICAL PULP 



221 



that some substitute must be found. With this end in view a 
long series of tests has been made on a practical scale by the 
Forest Service * and the pulps made run into paper and tested for 
printing qualities on newsprint presses. The following table 
gives the common and scientific names of the woods used, the 
yield of bone dry fibre from ioo cu. ft. of solid rossed wood and 
the color rating, No. i being the best color and No. 23 the poorest. 



Common name 



Scientific name 



Bone dry fibre 
per 100 cu. ft. 



Color 
rating 



Balsam fir 

Red fir 

White fir 

Alpine fir 

Amabilis fir 

Grand fir 

Noble fir 

Eastern hemlock. . . . 
Western hemlock. . . 

Tamarack 

Western larch 

Lodgepole pine 

Lodgepole pine 

Western yellow pine. 

Jack pine 

Loblolly pine 

White pine 

Engelmann spruce . . 

Sitka spruce 

White spruce 

Aspen 

White birch 

Black gum 



Abies balsamea. . . . 

' ' magnified .... 

" concolor 

" lasiocarpa. . . 

' ' amabilis 

' ' grandis 

' ' nobilis 

Tsuga canadensis . . . 

" heterophylla. . 
Larix laricina 

" occidentalis . . . 
Pinus murrayana l . . 

' ' murrayana 2 . . 

" ponder osa. . . . 

" divaricata. . . . 

' ' taeda 

" strobus 

Picea engelmanni . . . 

' ' sitchensis 

' ' canadensis .... 
Populus tremuloides . 
Betula papyrifera. . . 
Nyssa sylvatica 



Lbs. 
1910 

1915 

2000 
2060 
1870 
i95o 
1920 
2030 
2160 
2620 
2100 
1920 
2140 
2060 
2200 
2500 
1885 
2000-2250 
2100 
2400 
2200 
2950 
2600 



9 

20 
10 

1 
13 

5 
15 
19 
22 
21 
23 



14 
7 



16 

17 

4 



1 Wood from California. 



2 Wood from Montana. 



In these trials very little difficulty was experienced in pro- 
ducing pulp from the woods tested. With the conifers grinding 
could be done under practically the same conditions employed 
for spruce. All the substitutes, with the possible exception of 
noble fir and amabilis fir, require the use of more power per ton 
of pulp than does spruce. The best results were generally 
obtained by grinding on a somewhat dull stone with high pressure 
and rather slow speed. 

1 Bull. No. 343, U. S. Dept. of Agriculture. 



222 GROUND WOOD OR MECHANICAL PULP 

Of the woods tried all of the firs yield pulp suitable for news- 
print purposes; hemlock gives a short fibre and much care is 
necessary in grinding; western hemlock is much superior to 
eastern. Tamarack gives a good quality of pulp except for its 
color which is grayish green, while western larch yields a very 
inferior pulp, shivey and of poor color. The pines yield pulp 
which could be used for newsprint work though there is a tend- 
ency toward softness. The one exception is loblolly pine which 
gives an inferior pulp which would find use only as a filler. Of the 
hardwoods aspen gives a satisfactory pulp if a large amount of 
power is employed in grinding. When mixed with spruce it 
operates very well. White birch yields a short, but very fine 
fibre, which has a pinkish tinge; it could be used as a filler in 
certain grades of paper. Black gum gives a fibre resembling in 
many ways that from white birch. It is very short but forms a 
tougher sheet than coniferous fibres of the same length. This 
pulp is not promising for newsprint paper but could be used as a 
filler or mixed with pulp of a better grade. 

The ground wood process has received much attention from 
investigators with the object of producing fibre which could be 
used in making news paper without the addition of sulphite, 
Bache-Wiig * has patented a process whereby the blocks of wood 
are heated in a solution of salt and then ground as usual. As, in 
many cases, the salt does not penetrate the entire block the 
resulting pulp is a mixture of untreated and treated fibres. The 
claims for this process are that less power is required and the 
fibre is longer and stronger and of better color. According to 
another process 2 the wood blocks are placed in a digester which 
is partially evacuated, then treated under pressure with sulphur 
dioxide and finally cooked with water, salt solution or bisulphite 
liquor. Wood thus treated gives, on grinding, a pulp suitable for 
making news paper without the addition of sulphite. 

Henckel 3 proposes cooking the logs with a caustic soda solu- 

1 U. S. patent 913,679. 

2 Bache-Wiig: Paper, 1916, No. 21, p. 18. 

3 Henckel: Austrian patent 34,816. 



GROUND WOOD OR MECHANICAL PULP 223 

tion of 3 to 5 Be. for three or four hours under pressure and then 
grinding as usual. The claims for this process are better fibre, less 
power and greater yield. It is difficult to see how the yield 
can be increased by treating with a solution having such strong 
solvent powers as a caustic soda solution. 

A modification which has recently attracted much attention is 
that for producing white ground wood by the Enge process. 1 
According to this process the logs are placed in a boiler which is 
then completely filled with water. The temperature is raised by 
direct or indirect steam to 176 to 257 F., steam is shut off and 
hot or cold water pumped in to raise the pressure to 147 lbs. or 
more, which is maintained for five to eight hours. The higher 
the pressure carried the higher can the temperature go; good 
conditions are 230 F., and six hours at 147 to 176 lbs. per square 
inch. Following this treatment the grinding is completed on 
ordinary stones as usual. The advantage of this process is 
somewhat doubtful, for although the pulp can be made into news 
paper alone, yet the extra cost for steaming, labor, etc., just about 
counterbalances the saving in cost of sulphite fibre. 

With any method of grinding close control of the process is 
essential if a uniform product is to be made. A very simple 
method for obtaining such control is to examine the image of the 
fibres when thrown on a screen by means of a lantern. The pulp 
may be mixed with a little aniline dye so that a sharper image 
may be obtained. A little of the pulp is then placed between two 
glass plates in such a density that the individual fibres may be 
observed, and its image thrown upon a white screen. The best 
magnification is about 40 diameters and when enlarged to this 
extent it is very easy to tell the relative proportions of "fluff," 
long fibre, shives, slivers, etc. This method is in operation in 
one of the most progressive mills in Canada and is very highly 
recommended. Samples from each stone are examined every 
two hours and the condition of the stone and the work it is doing 
are thus accurately known, making it possible to sharpen the 

1 German patents 20,860 and 20,932, E VII, 55a. 



224 GROUND WOOD OR MECHANICAL PULP 

stone when it is necessary and keep the pulp much more nearly 
uniform. 

Another control test which is in actual use and is giving very 
good results is that of the sediment tester described by Fishburn 
and Weber. 1 In this test a mixture of 5 grams bone dry pulp 
and 500 c.c. of water is placed in a graduated tube with a woven 
wire bottom and the time required to drain down to a definite 
mark is noted. The standard time for news grade wood-pulp is 
80 seconds and if it is ground in such a way as to give a test of 
70 seconds trouble is experienced on the paper machine. 

The bleaching of wood pulp cannot be performed by hypo- 
chlorites or other oxidizing agents since all the lignin and other 
incrusting matters are still present. Its color can be consider- 
ably improved by treating with sulphurous acid or a bisulphite. 
This is regularly done in European practice by moistening the 
pulp with a solution of sodium bisulphite as it is wound up on the 
press roll of the wet machine. According to Schutz 2 about 2 to 
3 per cent is used. The action requires time and the color is not 
so bright as that of bleached chemical pulp. All woods are not 
equally susceptible to improvement in color by this process; 
hemlock and tamarack, for instance, are not so good as poplar and 
spruce. 

1 Paper, Oct. 11, 1916, p. 13. 

2 Schutz: Paper, Feb. 4, 1917, p. 64. 



CHAPTER VIII 
BLEACHING 

All of the commercial processes for isolating the fibrous cellu- 
loses for paper making fail to produce a perfectly pure material 
since it is always associated with a small amount of the in- 
crusting matter originally present in the raw material and gen- 
erally also with coloring matters, which either escaped destruc- 
tion during the process or were formed by it. The object of 
bleaching is the destruction or removal of such undesirable 
impurities so that the natural white color of the pure cellulose 
may become evident. The process of bleaching is essentially 
one of oxidation and the success attained depends on the fact 
that the accompanying impurities are attacked and resolved 
into soluble products much more easily than the comparatively 
inert cellulose of which the impure fibre is largely composed. 
Many different oxidizing agents can be utilized in the bleach- 
ing process and a number of them have been applied with more 
or less success, but practically all commercial work is performed 
by chlorine, or some of its compounds, which in the presence of 
moisture tend to liberate oxygen. 

Chlorine. Chlorine is a greenish yellow gas, darkening in 
color as the temperature rises. It has a pungent and irritating 
odor and cannot be inhaled as it attacks the membranes of the 
throat and nose. Its atomic weight is 35.457 and a liter of it 
at o° C. and 760 mm. pressure weighs 3.1 691 grams. One vol- 
ume of water at 15 C. and 760 mm. pressure absorbs 2.37 
volumes of chlorine. At 15 C. and 6 atmospheric pressure it is 
converted into a clear yellow liquid of specific gravity 1.33, 
which is not miscible with water. When perfectly dry it does 
not attack iron, which enables it to be stored and shipped in 

225 



226 BLEACHING 

wrought-iron cyclinders. Dry chlorine is also devoid of bleach- 
ing properties as may be shown by passing the dry gas over a 
piece of litmus paper, or a cloth dyed a delicate shade; so long 
as moisture is absent no bleaching action takes place, but on 
the addition of water the color is at once destroyed. 

Gas Bleaching. In bleaching with chlorine gas the material 
to be treated must be placed, while in a moist condition, in a 
receptacle which is capable of being tightly closed. It is then 
subjected to the action of the gas, either generated by means 
of manganese peroxide or obtained from some other source. If 
the material to be bleached is very shivey, gas bleaching mate- 
rially assists in the production of clean stock as it tends to 
resolve the woody matter more completely than does bleaching 
powder solution. It is also very efficient in removing metallic 
particles. Gas bleaching has in the past been applied to rag 
and rope stock, wood pulp, straw, etc., but little information is 
available to show how much of the gas is actually used up in 
the bleaching. Beadle and Stevens 1 cite a case of a cotton rag 
half-stuff which normally required 12 per cent of bleaching 
powder but in which a better color was produced by treatment 
with 2 per cent of chlorine followed by 2 per cent of bleach. 
In this case 2 per cent of chlorine replaces 10 per cent of bleach- 
ing powder, or is equivalent to 3.5 per cent of chlorine in the 
form of bleaching powder. Experiments by the author on a 
sample of soda hemlock which could not be satisfactorily 
bleached with hypochlorite solution showed that 4 per cent of 
chlorine followed by 5 per cent of bleach gave a good color 
and that in this case 2 per cent of chlorine was equivalent to 
3 per cent in the form of hypochlorite. In spite of its good 
bleaching efficiency the process is seldom used because of the 
difficulty of maintaining tight apparatus and the general in- 
convenience involved; it is never employed in this country. 

Hypochlorites. When chlorine is passed into an aqueous 
solution of an alkali, or alkaline earth, a hypochlorite or hypo- 

1 J. Soc. Chem. Ind., 1914, p. 727. 



HYPOCHLORITES 227 

chlorous acid is formed according to the equations: 

2 KOH + 2 CI = KOC1 + KC1 + H 2 
KOH + 2 CI = KC1 + HOC1. 

If it is passed into a suspension of calcium carbonate, hypo- 
chlorous acid only is formed: 

CaC0 3 + H 2 + 4 CI = CaCl 2 + C0 2 + 2 HOC1. 

The first bleaching compound known, eau de Javel, was 
made in 1789 at the Javel works near Paris by passing chlorine 
gas into a solution of crude potassium carbonate. In 1798 
Tennant patented a bleach liquor prepared by passing the gas 
into caustic soda or milk of lime and this method is still very 
largely employed where chlorine can be produced cheaply and 
the bleach solution used on the spot. 

According to Higgins 1 hypochlorites and hypochlorous acid 
bleach because of their readiness directly to produce oxygen 
and to a lesser extent because of the generation of nascent 
chlorine. As the bleaching with hypochlorous acid proceeds, 
hydrochloric acid accumulates and reacts with the hypochlo- 
rous acid according to the equation, HOC1 + HC1 = H 2 + Cl 2 . 
When a hypochlorite is used the acid formed is used in liberat- 
ing more hypochlorous acid. It has been shown experimentally 
that the removal of free hydrochloric acid from either hypo- 
chlorous acid or chlorine water by means of calcium carbonate 
results in an acceleration of the bleaching action. Higgins 2 
has also shown that the addition of calcium, barium or sodium 
chloride, or of sodium or potassium fluoride to a hypochlorite 
solution causes an initial increase in rate of bleaching, but that 
this acceleration soon ceases and the normal rate of bleaching 
ensues. This action is due to the formation of nascent chlorine: 
HOC1 + NaCl ±± NaOH + Cl 2 . The calcium chloride formed 
during the action of the bleaching powder is negligible but 
when calcium chloride is added during the process it always has 

1 J. Soc. Dyers and Colorists, 19 14, 30, 326. 

2 J. Soc. Chem. Ind., 1913, 32, 350. 



228 BLEACHING 

a stimulating effect. This effect of adding salt probably ex- 
plains in part the claims for greater efficiency which many 
observers have made for electrolyzed salt solutions since the 
latter always contain a large proportion of undecomposed 
chloride. 

Bleaching Powder. The bleaching solutions first prepared 
by Tennant proved difficult to keep and transport and in 1799 
he introduced a great improvement by absorbing chlorine gas 
in slaked lime, thus forming bleaching powder, which is still the 
most important commercial bleaching agent. 

The quality of the lime used in making bleaching powder is 
of importance, a fat lime which slakes quickly and gives a fine, 
light powder being most suitable since it absorbs the gas more 
quickly and gives a better keeping powder than a poorer lime. 
Careful slaking is essential since the total moisture in the chlo- 
rine and the lime should be about 28 per cent or about 4 per cent 
over that necessary to give calcium hydrate, Ca(OH) 2 . Well- 
made bleaching powder should be a pure white powder which, 
if of high strength, may contain some lumps. These, however, 
should be of the same quality as the powder and should not 
contain hard cores of calcium hydrate. In the air it absorbs 
moisture and carbon dioxide and is finally converted into a 
sticky, grayish mass. According to Lunge the composition of 

bleaching powder is best expressed by the formula, Ca <f • 

On dissolving the powder this is changed into Ca0 2 Cl 2 and 
CaCl 2 . 

The value of bleaching powder depends on the percentage of 
chlorine present as hypochlorite, or, as it is generally expressed, 
" available chlorine." Bleach made in cold weather may con- 
tain as much as 38 per cent available chlorine but in hot weather 
it is at times difficult to prepare it with even 35 per cent. In 
laboratory experiments it has been made with as high as 43.1 
per cent available chlorine. The powder gradually loses strength, 
even in the absence of air, while the presence of air, moisture or 
heat causes it to deteriorate much more rapidly. The shaking 



BLEACHING POWDER 



229 



incident to transportation also causes more loss than would 
occur under normal conditions of quiet storage, hence the 
strength is usually guaranteed only at the place of shipment. 
In 1886 Pattinson 1 completed a very careful series of tests to 
show the deterioration of bleaching powder. He stored three 
casks of bleach in a cave and tested them at intervals of a 
month for eleven months, at the same time keeping a record of 
the temperatures by means of maximum and minimum ther- 
mometers. This record shows the temperature to have been 
comparatively low and quite uniform during the entire period, 
the highest being 62 F. and the lowest 38 F. Tests of the 
samples taken from the casks showed a gradual and regular 
loss of available chlorine which at the end of the investigation 
amounted to about 3 per cent. The complete analysis of each 
of the cask samples at the beginning and end of the experiment 
is given in the table below: 



Jan. 29, 1885 



Jan. 5. 1886 



Available chlorine 

Chlorine as chloride 

Chlorine as chlorate 

Lime 

Magnesia 

Silicious matter 

Carbon dioxide 

Alumina, ferric oxide and oxide of 

manganese 

Water and loss 

Total chlorine 



37.00 

°-35 
0.25 
44.49 
0.40 
0.40 
0.18 

0.48 
16.45 



38-3° 
o.59 
0.08 

43-34 
0.31 
0.30 
0.30 

o.45 
16.33 



36 .00 
0.32 
0.26 

44.66 

o.43 
0.50 
0.48 

°-35 
17 .00 



33- 80 
2.44 
0.00 

43-57 
0.31 
0.50 
0.80 

0.40 
18.18 



36.10 
2 .42 
0.00 

42 .64 
0.36 
0.40 



17- 



32.90 

i-97 
0.00 

43-65 
0.38 
0.50 
i-34 

o-37 



37-6o 



38.97 



36.58 



36.24 



37-52 



34-87 



It is seldom that bleach can be stored for any length of 
time at a temperature as low as 6o° F., especially during the 
summer when the greatest loss of strength is likely to take 
place. It should, however, be kept in as cool and dry a loca- 
tion as possible and any damaged casks should be used first as 

1 J. Soc. Chem. Ind., 1886, 587. 



230 BLEACHING 

the consequent exposure of the powder permits more rapid 
deterioration to take place. Another factor which has a con- 
siderable influence on the rate at which the powder loses strength 
is the quality of the cask in which it is packed. The best casks 
are those made from oak staves which are about an inch in 
thickness. Lighter staves and other woods are often used but 
soft woods which shrink badly when exposed to the sun should 
be avoided as they permit entrance of moisture if the casks are 
subsequently exposed to rain. In recent years the powder is 
often packed in thin, sheet-iron drums which have been found 
to give fairly good satisfaction. As these are not intended for 
refilling they are made as thin as is consistent with sufficient 
strength for handling and they are therefore lighter 'and occupy 
less space than wooden casks. Such drums will, however, rust 
through in time and allow the bleach to deteriorate. 

The preparation of bleaching powder solutions has been care- 
fully studied by Carey and Muspratt. 1 They found that long 
agitation of the powder with water caused slow settling and a 
larger volume of sludge and that the solution of the calcium 
hypochlorite was as complete with twenty minutes agitation as 
it was in a longer time. The temperature was also found to 
exert an important influence as at higher temperatures the 
settling was more rapid and the volume of sludge less. It was 
found safe to prepare solutions at 90 F., but 75 to 8o° F. was 
considered better practice. The sludge, after drawing off the 
strong bleach solution, should be given a washing by filling the 
tank with water, agitating a few minutes and again allowing 
it to settle. The weak liquor thus prepared may be used to 
dilute the strong first liquor or for mixing with another charge 
of powder. The strength of solution usually prepared is 4.5 
to 5 Be., this together with the washings gives a liquor of 
about 3 Be. which is a satisfactory strength for practical work. 

The sludge, or residue, from dissolving bleaching powder con- 
sists almost entirely of calcium hydroxide but it is not possible 
to remove the last traces of available chlorine without excessive 

1 J. Soc. Chem. Ind., 1903, 674. 



BLEACHING POWDER SOLUTIONS 23 1 

washing. With careful work such losses should not be over 
0.3 to 0.4 per cent. The sludge should be tested for available 
chlorine at frequent intervals as considerable loss may occur if 
the washing is incomplete. The volume occupied by the sludge 
will necessarily vary with different powders and different meth- 
ods of dissolving but under normal conditions it should not 
exceed 5 cu. ft. per 100 lbs. of powder. 

A solution of bleaching powder is subject to decomposition 
of a nature similar to that taking place in the powder itself. 
This change is hastened by heat, light and air. Lunge and 
Landolt l examined the stability of bleach solutions and found 
that when kept in the dark and away from air no change took 
place in 24 days and only a very slight change at the end of 33 
days; when stored in the dark, but in open vessels, one-eighth 
of its strength was lost in ^^ days and when kept in diffused 
daylight 75 per cent of its strength was lost in the same time. 
Presence of acid or excess chlorine, or exposure to direct sun- 
light causes still more rapid decomposition. Tests by the author 
on a very strong bleach solution — 82 grams available chlorine 
per liter — prepared by absorbing chlorine in milk of lime, 
showed that when kept in a flask covered loosely with a watch 
glass and exposed to diffused daylight only 2 per cent of its 
strength was lost in eight days. Higgins 2 has compared bleach- 
ing-powder solutions with those prepared electrolytically, and 
with sodium hypochlorite prepared by treating bleach solution 
with soda ash, and found all equally stable. All of these in- 
vestigations point to the desirability of storing bleach solutions 
in tall, narrow tanks, where they will be exposed to light as 
little as possible. 

The action of bleaching powder solutions on metals has been 
studied by White. 3 He found that antimony and cadmium 
were not attacked, lead and zinc were acted on only very slowly 
because of impurities such as iron and arsenic, while aluminum 

1 Chem. Ind., 1885, 343. 

2 J. Soc. Chem. Ind., 191 1, 185. 

3 J. Soc. Chem. Ind., 1903, 132. 



232 BLEACHING 

was acted on very slowly in wire form but rapidly when present 
as filings. Nickel and iron were rapidly attacked with evolu- 
tion of oxygen and formation of the respective hydroxides, while 
copper was slowly attacked and tin very slowly, about one- 
twentieth of the rate of action on iron. The author's tests on 
strong bleach solutions showed that in five days the presence of 
metallic zinc in contact with the solution caused a loss of 10.5 
per cent of the available chlorine while lead caused a loss of 
3.6 per cent and ferric oxide 6 per cent. Solutions of similar 
strength kept for the same length of time away from contact 
with all metallic substances lost none of their available chlorine. 
Where electric power is available bleach solutions are often 
prepared by electrolyzing a strong salt solution and absorbing 
the chlorine in milk of lime. Such solutions have all the prop- 
erties of those made by dissolving bleaching powder. If a 
sufficient excess of lime is used and the temperature is not 
allowed to rise too high it is possible to prepare solutions con- 
taining 250 grams per liter of 35 per cent bleach with 96 per cent 
of the chlorine in the available form. Such solutions are of 
course too strong to use in actual bleaching operations but they 
are economical of storage room and may be shipped to consid- 
erable distances in tank cars. In cold weather very strong 
solutions of bleach occasionally deposit a considerable quan- 
tity of crystals which consist o'f solid calcium hypochlorite. 
Some of this solid hypochlorite is also present in the mud which 
separates during the preparation of solutions containing 225 
grams per liter, or more, of 35 per cent bleach. This crystalline 
form is very unstable and its preparation has never proved 
practical or desirable. In preparing strong bleach solutions 
there is occasionally a lot which turns pink. This was formerly 
supposed to be due to the presence of manganese but Tarugi l 
claims that it is caused by iron and has succeeded in causing it 
by warming a bleach solution to which a little soluble iron salt 
has been added. Elledge, 2 on the other hand, has proved that 

1 Chem. Centr., 1905, 584, 1902, 718. 

2 Elledge: J. Ind. Eng. Chem., 1916, 8, 780. 



ELECTROLYTIC BLEACH 233 

it can be caused by traces of manganese and it seems probable 
that it may be caused at times by either one of these substances. 

Electrolytic Bleach. Besides the various calcium hypochlo- 
rite solutions there are numerous devices for the electrolysis of 
salt solutions and the direct application of the sodium hypo- 
chlorite solutions thus obtained. The most celebrated of these 
is the Hermite process which originally employed a solution of 
magnesium chloride but in which salt was later used almost 
exclusively. According to this plan the solution was first elec- 
trolyzed and then passed through the material to be bleached 
and back to the electrolyzer, thus keeping up a continuous cir- 
culation. This continuous process can only be applied to rag 
stock as the impurities dissolved in bleaching esparto or chemi- 
cal wood pulp soon contaminate the solution to such an extent as 
to interfere with its proper operation. The Hermite process is 
probably not used in this country. 

Many other schemes for the use of electrolyzed salt solutions 
have been proposed and much has been said about the superior 
bleaching power of a pound of chlorine thus prepared over the 
same quantity in the form of bleaching powder solution. While 
these claims are undoubtedly made in good faith it seems prob- 
able that many are based on incorrect comparisons since tests 
of efficiency by bleaching for a given time and determining the 
residual bleach are not accurate unless exactly the same colors 
are produced. Ahlin : states that it is not true that active 
chlorine produced electrolytically will do more work than an 
equal quantity from bleaching powder, and Dorenfeldt 2 claims 
that unless brine is to be obtained almost free of cost or unless 
sodium carbonate is worth no more than quick lime an electri- 
cally prepared bleach liquor (sodium hypochlorite) cannot pos- 
sibly compete with bleach obtained from an electrical chlorine- 
soda process. 

There have been proposed from time to time other bleach 
liquors formed by the addition of magnesium, aluminum or 

1 J. Soc. Chem. Ind., 1902, 718. 

2 Papier Ztg., 1903, 215. 



234 BLEACHING 

zinc sulphate to a bleaching powder solution. These have the 
advantage of rapidity of action and except for their high cost 
would be useful in bleaching paper stock. The action of mag- 
nesium hypochlorite is purely oxidizing and it seems to have 
no tendency toward the formation of chlorinated products, while 
calcium hypochlorite shows this tendency quite strongly, espe- 
cially when acid is used. Because of their cost these solutions 
are practically never used except in isolated cases where per- 
haps a little alum is added to the beater to hasten the action. 

Principles of Bleaching. The general principles governing 
the practical application of the bleaching process have been 
carefully worked out by numerous investigators, who have 
studied among other factors the influence of concentration of 
stock, temperature of bleaching, and the accelerating effect of 
acids, air, beating, etc. 

The concentration of the stock when bleached is held by 
Baker and Jennison x to be one of the most important factors. 
This is doubtless true when the bleaching is conducted by add- 
ing an excess of bleach and removing the unused part at the 
end of a certain time. Under these conditions the proportions 
of stock and water would certainly exert a considerable influence 
on the color produced and the old saying "more water, more 
bleach" would hold good. If, however, a definite amount of 
bleach is added to the stock and the action allowed to continue 
until the bleach is exhausted then the amount of water used is 
practically without effect on the final color of the stock, though 
it has a great influence on the time required to use up the bleach. 
This is illustrated by tests on two sulphite fibres, one of which 
required 5 per cent and the other 13 per cent of bleach; when 
these were bleached at a concentration of one part of fibre in 
140 parts of water they required 21 to 22.6 hours to exhaust 
while at a concentration of one part in 23 the same point was 
reached in 15 to 15.5 hours. The color was, however, practi- 
cally the same in both cases. 

The temperature at which the bleaching is conducted has a 

1 J. Soc. Chem. Ind., 1914, 284. 



PRINCIPLES OF BLEACHING 235 

very pronounced influence on the results obtained, both as to 
color produced and time required in the operation. Cross and 
Bevan 1 state that esparto bleached at o° to 4 C. uses only 
80 per cent of the bleach consumed at 35 C. and gives an 
equal color. With sulphite spruce and soda poplar we have 
found that to exhaust a given amount of bleach at 40 C. re- 
quired eight to nine times as long as it did at 65 C. This extra 
speed was gained, however, at the expense of color, for the 
inferiority of the samples bleached at 65 C. was so marked 
that it would have been necessary to use fully 5 to 10 per cent 
more bleach in order to bring them to the standard color. 
Simonsen 2 in working with a sulphate pulp found that 7 per cent 
of bleach was sufficient at 13 C. but that if the temperature 
were raised to 35 C. it required 9 per cent of bleach to give the 
same color. Schwalbe claims that temperatures over 30 C. 
are to be avoided as bleach is lost through transformation into 
chlorate; this is quite probably one of the chief reasons for the 
poorer color obtained at higher temperatures. The maximum 
temperature which it is safe to use is variously stated by differ- 
ent authorities at from 68° to no° F. (20 to 43 C). No hard 
and fast line can however be drawn since it is often a question 
of adjusting the temperature so that a certain output may be 
obtained from a given equipment. In such cases it may be 
for a time better policy to increase the temperature rather than 
replace or enlarge the apparatus though it is certainly true that 
if the temperature rises much above 35 to 40 C. an appre- 
ciable portion of the bleach will be wasted. 

The effect of temperature on the time required for bleaching is 
well illustrated by the following results obtained in the author's 
laboratory on three different kinds of fibre. 

1 J. Soc. Chem. Ind., 1890, 450. 

2 Paper Trade J., Feb. 12, 1914. 



236 



BLEACHING 



Fibre 



Bleach used for 
standard color 



Hours required to exhaust bleach 



At 65° C. At 40 C. At 20 C. 



Sulphite 

E. B. sulphite 
Soda poplar... 



Per cent 

13.0 

5° 

"•5 



i-5° 
1.25 

i-33 



12.0 
10.8 
13.0 



192 



The rate at which bleach is consumed is also shown in the 
following table which contains the results of tests by the author 
as well as by Sindall and Bacon. 1 The figures show the per- 
centage of the added bleach which was consumed in the times 
noted. 



Fibre 


Soda poplar 


Soda poplar 


Sodai 


Sulphite > 


Sulphite 1 




n-5 
40.0 


n-5 

12 .0 


11. 7 

18.0 


14 
18 


8 


Temperature C 


18 


Time in hours 


Per cent of bleach consumed 


0-5 

1 .0 

i-5 

2 .0 

3° 
4.0 
5-o 
6.0 
7.0 
8.0 


63.8 
70.O 

72.5 
82.5 


5i-3. 
55-3 

71.7 

73-i 
77-5 
96.7 


33 -o 
44 

66.0 

70.0 

80.0 


3° 

55 

78 
90 


20 

33 
43 
49 
56 
63 
70 


11 .0 
71 .0 


IOO. O 





1 The Testing of Wood Pulp. 

Weight Lost on Bleaching. The loss in weight which all fibre 
undergoes on bleaching, because of the oxidizing and dissolving 
power of the bleach solution, is in accord with the observed facts 
regarding the influence of temperature. Since the higher tem- 
perature causes quicker action and gives poorer color due prob- 
ably to chlorate formation it would be expected that the attack 
on the fibre would be less with a consequent smaller loss in 

1 The Testing of Wood Pulp. 



WEIGHT LOST ON BLEACHING 



2 37 



weight. That such is the case is proved by the following results 
of experiments in which the fibre was bleached at different tem- 
peratures but with the same amount of bleach until the latter was 
completely used up. 



Fibre 


Percentage 
bleach used 


Loss in weight due to bleaching 




at 20° C. 


at 40° C. 


at 70° C. 


Sulphite 


13.O 

"5 


Per cent 
2.31 
I.89 
I.89 


Per cent 
2 .27 
1.66 


Per cent 


E. B. sulphite 


1 -97 


Soda poplar 


1.64 







If the fibre is treated with an excess of bleach, which is not 
all used up when the desired color is reached, then an increase in 
temperature would be expected to increase the loss in weight and 
Simonsen 1 has found this to hold true in the case of a sulphate 
pulp which lost 4.5 per cent of its weight when bleached at 20 C. 
and 6.1 per cent at 30 C. 

The amount of bleach used exerts a great influence on the loss 
in weight during the process and the chemical composition of 
the bleach solution probably also has a considerable effect. It is 
hardly to be expected that sodium, magnesium and calcium 
hypochlorites would all cause the same loss in weight and the 
presence of alkali or acid during the process would certainly have 
an influence. With calcium hypochlorite the effect of increasing 
the amount of bleach used is illustrated by the following data: 



Fibre 



Sulphite 

E. B. sulphite 
Soda poplar. . . 



Per cent 35% bleaching 


Loss in weight due 


powder used 


to bleaching 




Per cent 


13 


2 .27 


22 


1 


5i 


32 


5 


06 


5 


1 


66 


15 


3 


59 


25 


5 


72 


"•5 


1 


94 


20.5 


3 


69 


3°-5 


8 


°3 



1 Paper Trade J., Feb. 12, 19 14. 



2 3 8 



BLEACHING 



This has an important bearing on the cost per ton of bleached 
fibre, since in the production of very white stock not only is the 
amount of bleach increased, but the loss during the process also 
rises so that more fibre has to be used to produce a ton of finished 
product. In commercial fibres the loss due to the chemical 



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.30 
.25 
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.15 
.10 












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2 4 6 8 10 12 14 16 18 20 22 24 
% Bleach used 

Fig. 34 

action of the bleach may drop as low as i per cent for very easy 
bleaching stock or rise as high as 5 per cent for fibre taking 20 to 
22 per cent of bleach. In one case where a fibre lost 12 per cent 
of its weight when bleached and washed it was discovered that 
it had been washed in the blow pits with sea water and that 
about one half of this loss was due to the soluble constitutents left 
by the salt water. 



USE OF BACKWATER 239 

The rate at which bleaching eliminates the color of sulphite 
fibre is shown graphically in Fig. 34, which is plotted from 
Sindall & Bacon's book on the Testing of Wood Pulp. The 
measurements were made by means of Lovibond's tintometer on 
samples of pulp which had been treated with progressively larger 
amounts of bleach. This shows very plainly the comparatively 
rapid disappearance of the red and blue and explains why 
bleached pulp generally has a slightly yellowish tone. 

No very positive statement can be made in regard to the 
bleach required by various classes of paper making fibres since 
it depends so largely on the way the unbleached fibre was pre- 
pared as well as on the bleaching method employed and on the 
color obtained. At the present time the following figures are 
approximately correct: 

Rags 2-5 

Sulphite spruce 5-20 

Soda fibres 8-15 

Use of Backwater. The character of the water used in break- 
ing up the pulp preparatory to bleaching has an appreciable 
influence on the amount of bleach required. In many cases it 
has been recommended, and has been the practice, to use the 
water drained from the bleached pulp to make up another charge 
for bleaching. This is not to be recommended since it is attended 
with an increase in bleach consumption and a lowering of the 
color of the pulp. The greater bleach consumption is caused by 
the organic matter in solution or suspension, which continues 
to use up bleach when further portions are added. In a number 
of tests by the author this "yellow water" removed from engines 
of bleached pulp which were originally furnished entirely with 
fresh water was found to use up for each liter of water from 0.94 
gram of 35 per cent bleach in six hours to 1.53 grams in eighteen 
hours at 35 C. Since the ratio of water to stock was 30 : 1 in 
these tests it is evident that this bleach consumption would be 
equivalent to 2.8 per cent to 4.6 per cent of bleach on the weight 
of the fibre. Sindall and Bacon l found that at 3 2 C. the bleach 

1 Testing of Wood Pulp. 



240 BLEACHING 

used up by this residual liquor was 35.5 lbs. for 10,000 lbs. of 
water while at 49 C. it amounted to 112 lbs. These quantities 
would be considerably increased if the water were used over and 
over, thus permitting an increase in the concentration of the 
organic matter. The use of "back" or "yellow" water for 
furnishing the unbleached stock is therefore to be recommended 
only when it is comparatively rich in unused bleach and when 
the products of its action can be washed out before the final 
bleaching is commenced, as under any other circumstances its use 
is likely to cost more than it saves. An intermediate washing to 
remove the soluble products formed by bleaching is beneficial as 
it enables a better color to be produced than would otherwise be 
possible, especially with hard-bleaching pulps. When one-third 
of the bleach is used up before such washing and the rest after- 
ward it has been found in actual practice that about 90 lbs. of 
bleach gave the same results as 100 lbs. when all is added at once. 
The bleaching of paper stock is performed in engines, chests 
or drainers according to the equipment available or the personal 
preference of the operator. Rag stock is most often treated with 
the bleach solution in the engine and then emptied into large 
tanks or chests provided with false bottoms. In these the 
bleaching is completed and the exhausted bleach solution then 
allowed to run away; the stock may then be treated with dilute 
sulphuric acid to still further improve the color and finally 
washed with water. The process may be hastened by heating 
the contents of the beater, best before the bleach is added, since 
otherwise it is likely to cause local overheating with loss of 
bleach and formation of oxycellulose. Addition of acid also 
hastens the bleaching by liberating hypochlorous acid which is 
more vigorous in its action than hypochlorite. A number of acids 
have been proposed for this work, from sulphuric to acetic or 
even carbonic which it has been proposed to lead into the beating 
engine just under the roll. The known accelerating influence 
of agitation or beating is due doubtless in part to the presence of 
carbonic acid in the air. Only a small amount of acid should be 
used, as it is constantly regenerated, and it should be added in a 



SYSTEMS OF BLEACHING 241 

highly dilute condition as strong acid tends to liberate chlorine 
and cause the production of yellow chlorinated products. Treat- 
ment with acid is especially useful in bleaching shivey flax or 
linen and in treating rags which have been boiled in alkali and 
hence have accumulated basic matters which might be injurious 
at some future stage. 

Rags may also be bleached before reducing to half stock by 
washing the boiled rags and treating them in a tumbler with 
bleach solution; or they may be piled up in chambers and the 
warm bleach circulated through them. In the latter case they 
must be quickly drenched with cold water and transferred to the 
beaters as the fibres become tender if allowed to stand in contact 
with the bleach. Neither of these methods is so satisfactory as 
that of bleaching the half stock. 

Systems of Bleaching. Bleaching systems in general may be 
divided into two classes, one a rapid bleach in which an excess of 
fairly strong liquor is added and the excess removed as soon as 
the stock has reached the desired color; the other a slower 
process, using only a very slight excess and allowing it to prac- 
tically exhaust. The rapid bleach necessitates the use of the 
excess bleach liquor removed from the bleached stock, which has 
been shown to be uneconomical; it also requires more careful 
control since the higher temperature usually maintained and the 
stronger bleach solutions are more apt to cause oxidation of the 
cellulose and a consequent weakening of the fibre. The slower 
process is more economical of bleach but requires much more 
space for a given output and in the choice of a method the space 
available for the plant is frequently the deciding factor. In either 
method the amount of water used should be kept as low as pos- 
sible since this saves both bleach and time. The proportion of 
water to fibre will necessarily vary with the type of apparatus 
employed but with large chests furnished with good agitators it 
should be not much greater than 30 to 1. If the bleaching is 
done entirely in engines somewhat less water can be used, while 
in the Belmer bleaching apparatus the stock may be run at 5I to 
6| per cent density. 



242 BLEACHING 

Recognition of the advantage of using as little water as pos- 
sible is shown in Dobson's bleaching process in which the dry 
sheets of fibre are added to the bleach solution in a drum-like 
vessel which is then closed and rotated at two to four revolutions 
per minute for about three hours, when the bleaching is completed. 
The claims for this process are that it saves time, power and 
floor space and that the stock needs no washing or draining and 
is ready to use as soon as the bleaching is completed. While this 
process might be applied to wood pulp it is obvious that rags 
which have been cooked with lime could not be satisfactorily 
treated by it. 

The bleaching of fibres prepared by the soda process, whether 
from esparto, straw or any of the numerous woods now used, 
follows in general the same course as rag stock. Since the alka- 
line cooking treatment gives a well reduced fibre with a tendency 
toward an alkaline or basic condition it is safe to use a little acid 
in the process. This is best added in a well diluted condition 
after a considerable part of the bleaching has taken place and 
even then it must be used with care as these celluloses are more 
easily attacked than cotton or linen. When the color of these 
fibres has reached the desired point the bleach residues should 
be quickly removed lest the stock "go back" in color; this is 
especially likely to take place if the temperature is much over 
30 C. The removal of the exhausted bleach may be readily 
accomplished by running off the stock on some form of wet 
machine or on a press-pate. 

The treatment of sulphite fibre differs slightly from that 
accorded soda fibre since it has already a tendency toward acidity 
because of its method of preparation. Also it is usually not so 
thoroughly freed from lignin and incrusting matters as is soda 
fibre and hence is more liable to take up chlorine with the forma- 
tion of yellow chlorinated compounds. As acid increases this 
tendency it is not generally used with sulphite fibre, though it 
may be successfully employed by adding it about an hour after 
the bleach, washing the bleached fibre, which is frequently orange 
colored, and rebleaching with if to 2 per cent of bleach followed 



JUTE AND MANILA 243 

by a little acid. This treatment is unnecessarily complicated 
as most sulphite which is cooked with the idea of making into 
bleached fibre can be satisfactorily treated in a single process. 
As with wood pulp prepared by the soda process bleached sulphite 
is very apt to "go back" in color, or turn yellowish, if it stands 
in contact with exhausted bleach liquors, especially at elevated 
temperatures. For this reason it is quite important that the 
temperature be kept as low as is consistent with the desired 
rapidity of bleaching and that the fibre be freed from bleach 
residues as soon as the process is completed. 

In handling sulphite fibre it is frequently observed that a rose 
color develops on adding bleach. This is also caused by ferric 
chloride, potassium ferricyanide, mercuric chloride, potassium 
permanganate and potassium bichromate. 1 The exact reason 
for this phenomenon is not known but as the color produced is 
roughly proportional to the amount of bleach which the fibre 
requires it may be taken as giving an indication of the bleaching 
properties of the sample in question. This rose color is only 
transitory, as it disappears very quickly as the bleaching pro- 
ceeds, and has no permanent effect on the color of the fibre. 

Jute and manila fibres are particularly difficult to bleach since, 
in order to preserve their strength, they are generally only lightly 
treated with milk of lime and hence arrive at the bleaching process 
in a highly lignified condition. For this reason, and because the 
production of a high white seriously injures the strength of the 
stock, they are seldom bleached beyond a good cream shade. To 
hasten the action 4 to 5 per cent of alum is sometimes added but 
if the stock is heated this is particularly likely to cause the 
formation of yellow chlorinated compounds which defeat the 
object of the process. The bleaching of these fibres is usually 
conducted in the beater but in some cases they are dumped into 
drainers in which the last part of the bleaching proceeds slowly 
for several days. The chlorinated compounds mentioned, when 
treated with a solution of sodium sulphite, develop a strong 
magenta color. They are easily soluble in alkalis and may be 

1 J. Soc. Chem. Ind., 1896, 467. 



244 BLEACHING 

removed from the fibre by treating with a dilute soda-ash 
solution. 

Ground Wood. The treatment of ground wood, or mechani- 
cal pulp, so as to improve its color, is a problem which has occu- 
pied the attention of many investigators. Since the ground wood 
contains all the constituents of the wood itself, except a very 
slight amount of water-soluble matter, it is obvious that any 
treatment with hypochlorite would be out of the question, since 
40 to 50 per cent of the weight of the stock would have to be 
oxidized and dissolved before any good white color could develop. 
The first effect of adding hypochlorite to ground wood is the 
production of a red or brown shade which persists until nearly all 
of the incrusting matter has been destroyed. 

The color of ground wood may be somewhat improved by 
treating it with sulphurous acid, or bisulphite solution. This can- 
not be considered a true bleaching process as the coloring matter 
is not destroyed but merely masked temporarily and the color 
returns on exposure to the air for some time. Considering the 
results obtained sulphurous acid is too costly and the reagent 
usually employed is calcium or sodium bisulphite. One method 
of treatment is to employ about 2.5 per cent on the weight of 
dry fibre, diluted with 20 to 30 times its weight of water, with 
which solution the fibre is flooded from below so as to drive out the 
air. After allowing to stand for some time the solution is 
washed out. Another procedure is to spray the fibre with bisul- 
phite solution as it is taken from the wet machine and allow the 
whitening to take place in the moist laps. In this case no final 
washing is given. 

Antichlors. It is very, essential that the bleached stock going 
to the beaters should contain no active chlorine, which may 
readily be determined by means of iodide of starch solution. 
This may be prepared by boiling up a little starch with water and 
adding a few crystals of potassium iodide. A little of this test 
solution sprinkled on the pulp will, if the latter contains any 
bleach, develop a blue color varying from a faint color almost to 
a black according to the amount of bleach present. It is always 



ANTICHLORS 245 

best to test the stock being bleached rather than the water 
squeezed from it since if much bleach is present in the latter it 
may destroy the blue, while if the bleach is nearly exhausted the 
liquor sometimes fails to give a test though the stock still shows 
its presence. The difficulties encountered and the time required 
in washing out the last traces of bleach from the pulp have led 
to the use of various chemicals to reduce and render harmless any 
which may remain at the completion of bleaching. Such chemi- 
cals, from the nature of the work which they perform, are called 
antichlors. 

The one most commonly employed is sodium thiosulphate, 
Na 2 S 2 3 5 H 2 0, or "hyposulphite of soda" as it is generally 
called. This is added to the engine as a dilute solution after the 
stock has come to color. It acts on the bleach according to the 
following reaction: 

2 Ca0 2 Cl 2 + Na 2 S 2 3 + H 2 = 2 CaS0 4 + 2 NaCl + 2 HC1, 

in which the products formed are calcium sulphate, or "Pearl 
Filler," common salt and hydrochloric acid. According to 
Griffin and Little 1 if the solutions employed are very dilute the 
decomposition may take place in another direction as : 

Ca0 2 Cl 2 + 4 Na 2 S 2 3 + H 2 = 2 Na 2 S 4 6 + 2 NaCl + 2 NaOH 

+ CaO 

The products of either of these reactions are apt to exert a de- 
structive influence on the machine wires and their presence in the 
paper is fully as serious as that of the bleach which they are 
intended to eliminate. The use of thiosulphate is therefore not 
to be recommended. 

Safer antichlors to use are sodium sulphite, Na 2 S0 3 , and 
calcium sulphite, CaS0 3 , which according to the reaction, 

Ca0 2 Cl 2 + 2 Na 2 S0 3 = CaS0 4 + Na 2 S0 4 + 2 NaCl 
or Ca0 2 Cl 2 + 2 CaS0 3 = 2 CaS0 4 + CaCl 2 , 

give products which are much less harmful than those from 

1 Chemistry of Paper Making. 



246 BLEACHING 

thiosulphate. Because of the slight solubility of calcium sulphite 
the reaction in this case takes place rather slowly but it possesses 
the advantage that any excess acts as a filler and is in most 
cases quite harmless. 

Other antichlors which have been proposed are the ordinary 
sulphite liquor used in the manufacture of wood pulp; the mix- 
ture of calcium thiosulphate and polysulphide prepared by boil- 
ing sulphur with milk of lime; and hydrogen peroxide. The 
first of these is a rapid and efficient antichlor and in many cases 
it tends to brighten, temporarily, the color of the fibre. It must 
be used with considerable caution as any excess tends to set up 
an acid condition in the pulp with consequent injury to wires, 
driers and even the paper itself. The lime-sulphur mixture is 
probably even more injurious, since a considerable amount of 
free sulphur is precipitated on the fibres during the reaction and 
this, because of its finely divided condition, is gradually oxidized 
to free sulphuric acid, which renders the paper brittle by reason 
of the formation of hydrocellulose. The free sulphur also causes 
tendering of the machine wires through formation of metallic 
sulphides. Hydrogen peroxide is the safest of all the antichlors 
since it forms only water and free oxygen. It is, however, too 
expensive for commercial use. 

There are times when the use of an antichlor is of assistance but 
the regular employment of such an agent indicates inefficient 
bleaching methods since expense is being incurred in destroying 
a portion of the bleach which should be employed in doing useful 
work. In any well regulated mill it should be possible to elimi- 
nate the use of antichlors. 

Washing Bleached Pulp. The washing of bleached pulp to 
remove chlorides and the products of antichlor action is generally 
considered very necessary if durable paper is to be made from the 
stock. While this is probably true with regard to excess of 
antichlor and may have some influence in the case of the chlorides 
formed by the reduction of the hypochlorite yet it is felt that for 
the general run of book and magazine papers too much stress is 
laid on this point. This opinion is based on experiments carried 



PERMANGANATE BLEACHING 



247 



out with very thoroughly washed soda and sulphite pulps, and 
with part of the same lots which had been only very slightly 
washed after bleaching. These conditions were chosen as repre- 
senting the best and worst which were likely to occur in actual 
manufacturing operations. The two lots were beaten, sized and 
made into paper in the same way and pieces of the paper were 
then exposed to sunlight for three months and to temperatures of 
8o° to oo° C. for eight days. Neither of these tests showed greater 
discoloration in one case than in the other and both became 
brittle and unsized to about the same extent. The conclusion 
that slight washing is not likely to prove injurious to the dur- 
ability of the paper is put forward with some hesitation as it runs 
counter to generally accepted theories but from the above 
experiments no other conclusion can be reached. 

Washing will however improve the color of the bleached fibre 
by removing the yellow, soluble products of the bleaching action, 
and will, in large measure, prevent the brownish discoloration 
which is sometimes noticed on the edges of wet bleached pulp 
after storing for some time. According to Griffin and Little this 
is caused by the concentration of calcium chloride, due to more 
rapid evaporation on the edges, till it becomes strong enough to 
act on the fibre and form colored decomposition products. Our 
experiments with thoroughly washed, pure filter paper and a 
solution of chemically pure calcium chloride have shown that 
even relatively strong solutions fail to cause any discoloration 
even under very severe conditions of storage. The reason for 
these brown edges in commercial pulps is the incomplete removal 
of the soluble organic matter which is brought to the surface and 
edges of the pulp by capillary action and there concentrated by 
evaporation till its color becomes noticeable. 

Permanganate Bleaching. Permanganate of potash has often 
been proposed as a bleaching agent in place of the hypochlorites, 
and all sorts of claims have been made regarding its alleged 
superior efficiency. In presence of acid permanganate reacts 
according to the equation 

2 KMn0 4 + 3 H 2 S0 4 = K 2 S0 4 + 2 MnS0 4 + 3 H 2 +5 O, 



248 BLEACHING 

while in neutral solution the reaction taking place is 

2 KMn0 4 + H 2 = 2 KOH + 2 Mn0 2 + 3 O. 

Since the presence of acid causes too powerful an attack on the 
fibre it is necessary to bleach in neutral or slightly alkaline 
solution. 

Permanganate bleaching is extremely rapid and there is 
obviously no chance for the formation of chlorinated compounds. 
The permanganate should be added to the stock in dilute solution 
in order to avoid local formation of oxycellulose. When the 
bleaching has been completed it is necessary to remove the brown 
manganese peroxide by means of some reducing agent, most 
conveniently sulphur dioxide, or an acid sulphite. Beadle con- 
siders the sulphur dioxide to act as follows: 

Mn0 2 + S0 2 + 2 H 2 = Mn(OH) 2 + H 2 S0 4 , 
Mn(OH) 2 + H 2 S0 4 = MnS0 4 + 2 H 2 0. 

The Mn(OH) 2 being white is practically invisible and if the re- 
action goes no further may remain in the pulp and cause it to go 
back in color by absorbing oxygen and turning brown. All 
manganese peroxide should therefore be converted to the sul- 
phate. As all the alkali formed during the reduction of the 
permanganate must be neutralized before the manganese per- 
oxide can be dissolved it is evident that a considerable saving of 
sulphur dioxide can be effected by using some cheaper acid for 
this purpose. 

Beadle found by experiments on rags x that one pound of per- 
manganate did the same work as 10 lbs. of bleaching powder and 
concluded that the oxygen of the two substances acted quite 
differently. Our own experiments with sulphite and soda fibres 
show that in bleaching effect one pound of potassium per- 
manganate is equivalent to 1.854 lbs. of 35 per cent bleaching 
powder, while according to the oxygen evolved one pound should 
equal 1.93 lbs of bleach. It is evident, in the case of chemical 

1 Chapters on Paper Making, Vol. II, p. 117. 



EFFECT OF BLEACHING ON STRENGTH OF STOCK 249 

wood fibres, that the oxygen evolved by the two substances has 
the same bleaching power. 

The use of permanganate for conducting the entire bleaching 
process is more expensive than bleaching by hypochlorite and the 
necessity of acid for removing the manganese peroxide still fur- 
ther increases the cost. Even when the greater part of the 
bleaching is done by hypochlorite and the final treatment only is 
with permanganate the increase in cost is out of all proportion to 
the gain in whiteness. For these reasons permanganate is seldom 
employed in commercial work. 

Sodium peroxide and perborates, persulphates, etc., have also 
been proposed as bleaching agents but they are never used in 
this country. In fact von Possanner x has shown that sodium 
peroxide is of little value for bleaching rag stock, since even 
when excessive amounts are used only a partial bleaching takes 
place. Moreover, if employed in too strong solutions, it attacks 
the fibre and forms oxycellulose. 

Effect of Bleaching on Strength of Stock. The bleaching of 
paper stock induces in it a two-fold change since it affects both 
its physical and chemical properties. Experiments made by 
Frohberg 2 led him to conclude that bleaching very greatly 
reduced the folding strength in comparison with that of paper 
made from the unbleached fibre. In nine samples of sulphite 
which he tested this reduction in strength varied from 29.8 to 
62.7 per cent of the strength shown by the unbleached fibre. 
The breaking length was affected much less than the folding 
strength, being reduced by only about 7 to 12 per cent. A slight 
overbleaching was found to reduce the strength and durability 
of the paper to a still greater extent. 

Our own very carefully conducted experiments entirely con- 
tradict those of Frohberg. Starting with the unbleached fibre, 
samples were beaten and made into hand mould sheets under 
standard conditions. Portions of the same fibres were then 
bleached with two different amounts of bleach, the lowest being 

1 Wochbl. Papierfabr., 44, 3161. 

2 Ibid, 44, 3599. 



250 



BLEACHING 



that which would give a good standard white shade, and the 
bleached fibre beaten and made into sheets as before. The air 
dry sheets were then subjected to folding tests on the Schopper 
folder, and to bursting tests on the Ashcroft tester. The results 
on three different fibres are as follows: 



Sulphite No. I 



Folding test . 
Ashcroft test. 



Unbleached 



i-9 

18.3 



13 per cent 
bleach 



15-8 

35-2 



Folding test. 
Ashcroft test. 



Unbleached 



i-5 
21.3 



1 1. 5 per cent 
bleach 



O.O 

20.2 



22 per cent 
bleach 



II. 9 

30.9 



Sulphite No. 2 




Unbleached 


S per cent 
bleach 


IS per cent 
bleach 


Folding test 


2.9 
21 .1 


15.O 
34-o 


4-4 
32.4 






Soda, poplar 







20.5 per cent 
bleach 



0.0 

9-2 



With the sulphites the bleached fibres possess greater strength 
than the unbleached even when bleached to an extremely white 
color, while the strength of the soda fibre is reduced by bleach- 
ing. A partial bleaching with hypochlorite followed by per- 
manganate was found in every case to give a stronger fibre 
than if the bleaching were carried to the same point by hypo- 
chlorite alone. 

In this connection it is interesting to note the results obtained 
by O'Neill x on cotton cloth before and after bleaching. He 



1 Griffin and Little: Chemistry of Paper Making, p. 288. 



EFFECT ON CHEMICAL PROPERTIES 



251 



measured the weight required to break a single thread with the 
following results: 





Before bleaching 


After bleaching 


No. 1 cloth, weft threads 


Grains 

1 7 14 

3140 
3407 
3512 


Grains 
2785 


1 " warp " 


" 2 " " " 


3708 


'3 " " " 




4025 



In three out of four cases there is a distinct increase in strength 
due to bleaching. 

In our opinion it is safe to conclude that the folding and 
bursting strength of sulphite is not injured by bleaching but 
that with soda poplar the bleaching process does occasion a 
loss in strength. 

Effect on Chemical Properties. The two changes in the 
chemical properties of the fibre which are most likely to be 
caused by bleaching are the formation of oxycellulose and chlori- 
nated cellulose. If acid is used hydrocellulose is also likely to 
be formed locally. 

Griffin and Little 1 claim to have found between 5 and 6 
per cent of chlorinated cellulose in a bleached sulphite pulp of 
good color, while Cross and Bevan 2 showed that during the 
bleaching of wood pulp and esparto chlorine combined with the 
residual non-cellulose constituents, forming chlorinated com- 
pounds some of which remain fixed on the fibres after washing. 
According to these statements the presence of chlorine in a 
bleached pulp would not necessarily indicate insufficient wash- 
ing. Contrary to these opinions Schwalbe 3 finds that when 
cellulose is bleached by hypochlorites, whether in acid or alka- 
line solution, the amount of chlorine which combines with the 
substance of the fibre is quite negligible. In the case of sul- 
phite cellulose there is, however, a small quantity of chlorine 

1 Chemistry of Paper Making, p. 286. 

2 J. Soc. Chem. Ind., 1890, 450. 

3 Chem. Ztg., 1907, 31, 940-941. 



252 BLEACHING 

absorbed. Further work by the same author x was carried out 
with both calcium and sodium hypochlorite, in neutral and 
acid solutions and in industrial proportions and in excess. After 
bleaching the sulphite cellulose was washed, dried and carefully 
analyzed. The total chlorine in the bleached pulps from these 
tests varied from 0.051 to 0.114 per cent and of this 0.047 to 
0.071 per cent was present in combination with organic matter, 
the rest being combined with the constituents of the ash. In 
spite of these figures Schwalbe concludes that no appreciable 
chlorination of the pulp takes place and that the products of 
bleaching are removed during the process of washing. 

Besides the slight chlorination which may take place during 
bleaching there is a quite appreciable formation of oxycellulose. 
An approximately quantitative estimation of the amount of 
hydro- and oxy-cellulose formed may be made by determining 
the loss in weight of the thoroughly washed, bleached fibre 
when boiled in 0.25 per cent solution of caustic soda, or by 
means of Schwalbe's "copper number" method. 2 This latter 
method is a determination of the amount of copper reduced by 
the fibre on boiling with Fehling solution under carefully regu- 
lated conditions and the "copper number" is the number of 
grams of copper which would be so reduced by 100 grams of 
absolutely dry fibre. 

Using the two methods to study the effect of various bleach- 
ing conditions the following data were collected from experi- 
ments on two samples of sulphite and one of soda. All figures 
are based on the materials as weighed out for analysis and are 
not reduced to a common basis. 

These figures demonstrate that the more bleach used, and 
hence the whiter the product, the greater will be the attack on 
the cellulose itself. They also show clearly that permanganate 
causes much less oxycellulose formation than an equivalent 
quantity of hypochlorite. 

1 Z. angew. Chem., 1908, 21, 302-303. 

2 Z. angew. Chem., 23, 924 (1910), or Chemie. der Cellulose, p. 625. 



EFFECT ON CHEMICAL PROPERTIES 



253 





Copper number 


Loss in weight on 
boiling with 0.25 
per cent NaOH 


Sulphite No 
<< << 

<< << 

«« << 

<< 11 

Sulphite No 


z 
1 
1 
1 

1 

2 
2 
2 
2 

un 

{ 


unbleached 


} 
} 


2.56 
2.8l 
3-5i 
7-13 

4-13 

3-i8 
2.36 
4-99 
7-99 

0.72 

3 -°4 

6.70 

10.30 

4.20 


Per cent 


13 per cent bleach 

22 ' " " 

32 " " 

/13 " 

t 5.4 " KMn0 4 ... . 

unbleached 


10.9 
14.2 

21 .7 

15-3 
13.0 


5 per cent bleach 


10.2 


11 11 


tit " " 


17.4 


11 11 


2< " " 


25.2 


Soda poplar 

11 11 
<i 11 

11 11 


bleached 


i-5 


[i .5 per cent bleach 

20. s " 

3°-S 

"•5 " " 

5.4 " KMn0 4 


10. 5 
22 .0 
27.7 

13 -4 



By this same method of study Schwalbe has proved l that 
acid bleaching attacks cellulose more than alkaline, both in hot 
and cold bleaching. His results are: 





Copper number 




Alkaline bleach 


Acid bleach 


Hot 

Cold 


2.86 
2.77 


3-54 
4-23 



In some commercial sulphites, particularly those which are 
slightly undercooked and hence hard to bleach, it is difficult 
to obtain the pure white which is desired and occasionally the 
attempt is made to mask the remaining yellow color by the 
careful use of blue. Any such improvement in color serves 
only to disguise the true value of the pulp and the practice 
should be strongly discouraged. The addition of blue can im- 
prove the color only when the bleached pulp has a yellow tint 



1 Wochbl. Papierfabr., 39, 2273. 



254 BLEACHING 

as well-bleached pulps which have already reached a good de- 
gree of whiteness are made distinctly gray by the addition of 
blue and pink. If any considerable amount of blue has been 
added to the pulp it is generally quite noticeable, especially on 
looking through the suspected sample. When a smaller amount 
has been used its presence may usually be detected by rolling 
the sample into a tube and looking through it, in which case 
the multiple reflections of the light before reaching the eye 
intensify the color. 

There is a tendency with all bleached fibres to change some- 
what in color when kept for any length of time and while the 
alteration which takes place is slight and the chemistry of the 
process obscure, yet experiments have brought out some inter- 
esting facts. It has been shown that bleached sulphite which 
has been stored in well-seasoned hard-wood or tin receptacles 
hardly changes in color within six months, while similar samples 
stored in pine-wood boxes became somewhat yellower in the 
same time. Direct exposure to sunlight gives sulphite a red- 
dish tone while if part of the sheets are protected from the light 
by black paper the portions thus protected become much yel- 
lower than the fibre before exposure. Soda fibre is more sus- 
ceptible to these changes than sulphite and the more highly 
bleached the fibre the more rapidly it appears to deteriorate. 
These facts have a distinct bearing on the preservation of stand- 
ard samples of bleached pulps and indicate the precautions 
which should be taken in studying the changes which take place 
on exposure to light. 

Testing Bleaching Powder. In testing bleaching powder the 
first requisite is a fair sample. This should be obtained by 
boring a hole through the side of the cask midway between the 
ends or through the head near the centre, and inserting a sampler 
two or three inches into the bleach. The first sample should 
be rejected and the sampler again inserted as far as it will go, 
the sample thus obtained should be placed at once in a glass 
fruit jar which must be closed until the next cask is sampled. 
Every third or fourth package should be sampled, according to 



TESTING BLEACHING POWDER 255 

the size of the shipment, but in no case should less than 20 
per cent of the total packages be opened. 

The sample should be well and quickly mixed, breaking up 
any lumps with a stout glass rod, and 10 grams weighed out, 
put in a porcelain mortar, a little water added and the mixture 
rubbed to a smooth cream. More water is mixed in with the 
pestle, allowed to settle a little while and then poured off into a 
liter flask; the sediment is again rubbed up with water, and 
the process repeated till the whole of the sample has been trans- 
ferred to the flask and the mortar washed quite clean. The 
flask is then filled to the mark, thoroughly shaken and 50 c.c. 
at once removed with a pipette and placed in a beaker or cup. 

N 
To this solution ■ is then added standard — arsenite solution 

5 
until a drop of the mixture taken out with a glass rod and 
brought in contact with potassium iodide starch solution gives 
no blue color. The percentage of available chlorine may then 
be calculated by the formula: 

cubic centimeters arsenite solution X 0.7092 X 20 _ jper cent 

grams bleaching powder taken [ available CI. 

The analysis may also be carried out by adding an excess of 
arsenite solution to the bleach and titrating the excess with 
standard iodine solution. This involves the use of another 
standard solution and is no more accurate than Penot's method 
as outlined above. 

The standard — arsenite solution is prepared by dissolving 

exactly 9.9 grams of the purest, powdered, sublimed, arsenious 
oxide in about 500 c.c. distilled water in which 40 grams pure 
sodium carbonate have been dissolved. In order to accomplish 
this it is necessary to heat the mixture on the steam bath. In 
spite of using the highest purity chemicals it is generally neces- 
sary to filter the solution, which is afterwards cooled and made 
up to a liter. The strength of this solution is best ascertained 
by titration against a standard iodine solution. 



256 BLEACHING 

The starch-paste indicator may be made according to the fol- 
lowing formula which has been found to give excellent results. 
Mix three grams of potato or arrow root starch to a thin cream 
with cold water and pour into 250 c.c. of vigorously boiling 
water. Cool, add a solution of 1 gram potassium iodide and 
1 gram crystallized sodium carbonate and dilute to 500 c.c. 



CHAPTER IX 
SIZING 

For some purposes papers are required to be porous and 
absorbent, in order to allow the passage of fluids, as in filter 
paper, or their rapid absorption as in blotting paper, but for 
most applications, which imply the use of ink of some kind, 
it is desirable that they be more or less non-absorbent. This 
is particularly essential in the case of writing papers which 
come in contact with very fluid inks, and in papers which are 
to be used for coating, and it is even considered of importance 
in printing papers though the nature of printing ink is such 
that good letter-press work can be done on an unsized or water- 
leaf paper. Since the absorbent power of paper depends on 
the capillary action of the fibre surfaces and on the spaces 
within and between the fibres, it is necessary, in order to make 
the paper non-absorbent, to coat the fibres with some substance 
which will offer resistance to the passage of ink. This object is 
accomplished by various methods of sizing. 

The degree of sizing and the nature of the agents employed 
depend upon the use to which the paper is to be put. For 
news paper, on which the ink must dry very rapidly and almost 
wholly by absorption, the sizing must be slight so that capillary 
action may not be prevented; for book papers the sizing is 
usually harder than for news, not because the inks used are 
more easily absorbed, but because the sizing makes the paper 
more satisfactory for general service; for lithograph papers the 
sizing must be still harder because the paper becomes moistened 
during printing, while for writing papers on which very fluid inks 
are used the sizing must be particularly hard so that the ink 
may not spread and the lines become blurred. In the days 

257 



258 SIZING 

of hand-made papers the sheets were sized by dipping them 
into a tub of gelatine solution and the process was known either 
as tub or animal sizing from the nature of this operation. A 
modified form of this process is still employed and as it con- 
sists essentially of the deposition of a layer of the sizing mate- 
rial on the surface of the paper it might well be spoken of as 
surface sizing. 

This method of sizing is too slow and expensive for the great 
bulk of modern printing papers and for such other processes 
have been devised. Most of these depend upon the precipita- 
tion on the fibres of some material which on drying renders the 
sheet either repellent or resistant to moisture and as this opera- 
tion generally takes place in the beating engine it is usually 
called engine sizing. 

Surface Sizing. Numerous materials have been proposed 
from time to time for use in surface sizing but practically none 
are used in appreciable quantities except glue and starch and of 
these much more of the former is consumed than of the latter. 
For high-grade papers the best of glue, known as gelatine, 
should be used. These two terms are often indiscriminately 
applied, which is quite natural since gelatine may be considered 
as a highly purified glue which has been made with especial care. 

Pure gelatine is a colorless, odorless, nearly transparent, nitroge- 
nous substance which is insoluble in cold water but which 
swells and absorbs three or four times its weight when soaked 
in it. In hot water it dissolves readily and a strong solution 
sets to a firm jelly on cooling, even as little as 1 per cent giving 
a gelatinous mass. The purest commercial form of gelatin is 
isinglass which is made from the swimming bladders of various 
kinds of fish; below this in quality are the different grades of 
hide glue and still further down the scale are the bone glues. 
Many of the glues are excluded from sizing work because of 
their poor color and others because of their low gelatinizing 
power. 

In most instances it is better for the paper maker to purchase 
a gelatine or glue of standard quality than it is for him to try 



SURFACE SIZING 259 

and make it. He is likely to get a more uniform product and 
moreover it is claimed that size made from air-dried glue is 
superior to that made from the original jelly. The gelatine 
which gives the firmest jelly is considered the best sizing agent 
and as a general rule the higher priced gelatines will be found 
the cheapest in the end because of their greater efficiency. A 
gelatine of high gelatinizing power gives a solution with a low 
specific gravity, while with low-grade glues the reverse is 

true. 

The strength of solution used in sizing generally varies be- 
tween 4 and 7 per cent and the temperature at which it is applied 
may range from 85 to i2o°F. To this solution alum is fre- 
quently added to act as a preservative and aid in preventing 
spoiling of the sized paper in damp air. On adding the alum 
the glue solution thickens, and as the amount is increased it 
may almost form a jelly; strangely enough, however, if still 
more alum is added the solution becomes thin again and may 
even be more fluid than the original solution. This property 
offers a convenient means of controlling the penetration of the 
paper by the size, since this depends in part on the fluidity of 
the solution. The influence of alum added to the gelatin is 
shown in the following table 1 which gives the percentage of 
gelatine, based on the original dry paper, absorbed from a 5 per 
cent solution by papers sized with different amount of rosin. 

Percentage of rosin size 0.0 0.5 1.0 1.5 2.0 2.5 

Gelatine absorbed, no alum used 12. 1 10.9 8.9 8.0 7.2 6.5 

Gelatine absorbed, 8 per cent alum used 10.2 9.1 7.5 6.5 5.7 5.2 

Another substance occasionally added to the size solution is 
soap, which is claimed to have a certain lubricating effect on 
the fibres, to improve the opacity and to disguise the color 
of poor glue. The soap is dissolved to a clear solution in water 
and added to the glue solution before the alum, the addition of 
which decomposes the soap. Not every kind of soap is suitable 
for this work as its nature must be such that the addition of 

1 Cyster: Paper, May, 1915, p. 18, from World's Paper Trade Review. 



260 SIZING 

alum produces a fine emulsion rather than a curdled mass of 
fatty acids. 

The mechanical operations involved in surface sizing sheets 
of paper are of a comparatively simple nature; the sheets are 
suspended in a vat of the hot size till the air is expelled, the 
excess of size is removed by pressing and the sheets are hung 
up to dry. The immersion of the sheets is sometimes accom- 
plished by feeding them between endless felts into the size 
solution in a vat which must be long enough to give time for 
the air to escape from the paper. As applied to waterleaf 
papers this process is expensive because of the cost of handling 
single sheets and because of the large amount of size absorbed. 
This latter depends on the viscosity, temperature, and strength 
of the glue solution and upon the condition of the paper. Free 
stuff absorbs more glue than wet beaten stock, while bone dry 
paper absorbs it less rapidly than that with an appreciable 
amount of moisture. 

In this country practically all surface sized paper is made as 
a part of the paper machine operation by leading the web of 
paper through a trough filled with the size which is maintained 
at the desired temperature by continual circulation to and from 
the supply tank. This method enables the paper to be engine 
sized with rosin and partially dried by passing over a few cylin- 
ders before reaching the size trough so that the amount of glue 
absorbed is materially reduced. If, after removing the excess 
of size by squeeze rolls, the paper is reeled up and allowed to 
season a short time before drying the sizing is improved, but 
in many cases it passes directly from the squeeze rolls to the 
driers which are skeleton drums around which the paper passes 
and within which are fans to keep up a circulation of air. 

The drying of animal sized papers is a matter of particular 
importance since the quality of the product depends largely on 
this operation. It is desirable to dry slowly, without agitation 
and at a temperature below that required to liquefy the jelly so 
that the problem is really that of drying a jelly rather than a 
solution. Loft drying is the best but the slowest and most 



SURFACE SIZING 261 

expensive, the festoon arrangement used in drying coated papers 
gives fair results but is not perfect, while if the paper is dried on 
a steam cylinder the glue has little sizing power since individual 
fibres only are coated and the interstices are vacant. Papers 
dried on the skeleton drums are subjected to so much vibration 
from the fans that the surface tends to crack and the product is 
therefore inferior to loft dried paper. If, after drying, the sizing 
is found to be defective it may sometimes be improved by 
wetting and again drying. The temperature of drying depends 
in part on the atmospheric humidity. If this is low the drying 
takes place rapidly and a correspondingly low temperature may 
be employed but if the humidity is high the temperature must 
be raised to permit evaporation to take place. The upper limit 
is set by the liquefaction of the sizing, which in general may be 
said to take place at lower temperatures with the poorer grades 
of glue than it does with gelatines. 

Surface sizing makes paper stronger and firmer and gives a 
better surface for writing than does engine sizing. Its effect is 
reduced by the subsequent operations of calendering, rolling or 
plate glazing which explains the fact that papers with a rough 
surface are more easily hard sized than those which are highly 
glazed. 

The operation of surface sizing with glue, while apparently 
a simple one, is in reality one of the most difficult and uncertain 
of all those carried out by the paper maker, since the gelatine is 
influenced to so great an extent by atmospheric conditions and 
its absorption is so dependent on the physical and chemical con- 
ditions of the paper employed. 

The tests to which glue or gelatine for surface sizing should be 
subjected are those for grease, acidity, ash, added alum and firm- 
ness of jelly. The methods for the first two are given in the 
chapter on coated papers. The ash may be determined by 
burning out a weighed sample in a porcelain crucible and weigh- 
ing the residue which should then be examined for alumina by 
the usual qualitative procedure. The presence of the latter 
indicates that the jelly test may not be a just criterion of the 



262 SIZING 

sizing value of the glue since it is probable that alum has been 
added to increase the thickness of its solution. The jelly strength 
may be found by comparing that formed from a definite strength 
of solution with that from standard samples similarly treated. 
It may be determined numerically by preparing jellies from the 
same strength of solution and noting the time required for a 
definite weight to penetrate the jelly a given distance or by 
determining the force required to remove a plunger round which 
the jelly has been formed. 

Starch. This material is used in sizing both as a substitute 
for animal size and in the engines. 

For surface sizing the solutions of the untreated starches are 
too thick to be applied in the ordinary manner or if they are 
reduced to the proper consistency so much water has to be used 
that enough starch to be effective is not present. For this 
reason the chemically treated, or so-called modified, starches are 
used for this work. These are dissolved by boiling in water and 
are applied, either with or without the addition of soap, wax or 
other chemicals, in much the same manner as animal size. Used 
in this way they give a firmness and rattle to the paper but they 
are not so effectual in sizing against writing ink as are animal 
sizes. This is probably due in part to the hygroscopic nature of 
starch and partly to the fact that it does not form a jelly on cooling 
and hence does not fill up the spaces between the fibres as does 
gelatine. 

For use in the beating engines various kinds of starch are 
available but the one used is generally that which can be obtained 
most cheaply, due regard being paid to quality. For this reason 
corn starch is used almost entirely in this country while in 
Europe potato starch is largely employed. The starch is added 
to the engine either in the raw condition or after boiling with 
water to form a paste. The retention of the raw starch is un- 
doubtedly greater than that of the boiled but its effect in harden- 
ing the paper may not be any greater since in order to accomplish 
this it must be gelatinized during the passage of the paper over 
the driers. Examination of papers made from stock containing 



STARCH 



263 



raw starch shows that many granules are not even swollen and 
such can have little value except as a filler. 

Because of the difficulty of accurately determining starch in the 
presence of cellulose little definite information is available as 
to the percentage retained. It has been shown by Lutz * that 
the retention varies with the kind of starch and the condition 
when added. With hand-made papers prepared from stock to 
which 10 per cent of starch had been added he obtained the 
following retentions: 





Kind of starch 




Retention when added 




Raw 


Boiled 


Potato 


Per cent 

73-6 
71.7 
53-4 • 


Per cent 
46.2 
58.3 
58.9 


Wheat.. . 




t 


Rice 



It is interesting to note that with raw starch the larger grains 
are retained better while if the starch is boiled the better reten- 
tion occurs with those starches which give the stiffest pastes. 
It is very doubtful if such high retentions as the above can be 
expected in the case of machine-made papers where the chances 
for loss are so much greater. 

Starch used in the beating engine hardens the paper, prevents 
dusting, increases the strength and tends to keep down the fuzz 
caused by insufficiently beaten stock. It probably increases the 
retention of filler very slightly but the gain in loading is not 
great enough to pay for the starch required. It cannot be con- 
sidered a sizing agent in the same sense as rosin for it imparts no 
waterproof qualities. 

There has recently been exploited a so-called sizing process, 
using starch and silicate of soda, in which the starch granules are 
swollen by heat in the presence of the silicate solution. The 
theory is that the silicate penetrates the starch granules as they 
swell and that when alum is added the silicate is thrown down 

1 Papier Ztg., 1908, pp. 1098 and 1142. 



264 SIZING 

and carries the starch, with it. This process was claimed to 
retain all the filler, increase the strength of the paper, and give 
a better printing sheet. Practical trials on a large scale have 
shown that it does not appreciably increase the retention of 
filler but that it does give a stronger paper. In one run, that 
part sized with silicate-starch was 15 to 18 per cent stronger than 
that in which no starch or silicate was used, while in another 
thinner order the gain in strength was 38 to 46 per cent. On the 
whole the results by this process appear to be in no way superior 
to those obtained by adding starch and silicate separately to the 
engine. 

Rosin. This material is used in engine sizing to a greater 
extent than all other sizing agents together. It is obtained as a 
residue after distilling off the volatile portion from crude turpen- 
tine which is obtained in this country largely from the longleaf 
pine. Since the crude turpentine contains sand, bark, chips and 
other dirt these materials are always to be met with in commer- 
cial rosin. The point to which the distillation of the turpentine 
has been carried influences the color of the rosin, the higher the 
temperature the darker being the product. It also, to a certain 
extent, determines the commercial grading of the rosin since the 
grade depends on the color. Letters are used to denote the 
quality of the rosin, A being nearly black, while the lightest 
colored, W.W., or water white, is pale yellow. The medium 
grades, F and G, are those most commonly employed in paper 
sizing, and are considered to give better results than those of 
lighter color since the higher temperature of distillation insures 
the presence of less pitch. 

Rosin, or colophony, is a transparent or translucent resin, 
nearly tasteless, very brittle and showing a conchoidal fracture. 
Its specific gravity is 1.07 to 1.08. It softens at 70 to 8o° C, 
becomes semi-fluid in boiling water and melts completely at a 
somewhat higher temperature. It is insoluble in water but easily 
soluble in methyl and amyl alcohols, acetone, ether, chloroform, 
carbon disulphide and fixed and volatile oils. Because of its 
acid nature it dissolves readily in solutions of the alkalis forming 



ROSIN 265 

salts which are similar to those of the higher fatty acids or 
soaps. 

Rosin contains practically no ash. Its acid number varies 
from 155 to 175 and averages about 164; this corresponds to 
83.4 to 93.8 per cent of acid of the formula C20H30O2. The unsa- 
ponifiable matter present ranges from 4 to 10 per cent. Accord- 
ing to Schwalbe and Kiiderling, rosin contains from 0.1 to 6.7 per 
cent of matter insoluble in petroleum spirit. This insoluble mat- 
ter is formed very rapidly when powdered rosin is exposed to 
sunlight and as it is friable and devoid of sizing power its amount 
should be as low as possible. Colophony varies more or less in 
chemical composition but its chief constituent is a monobasic 
acid of the formula C20H30O2, variously spoken of as abietic, sylvic 
or pimaric acid. 

Because of the growing scarcity of rosin and its increasing price 
considerable attention is being paid to its preparation by extrac- 
tion processes from the "lightwood" and stumps of longleaf pine. 
There are on the market a number of rosins prepared in such 
ways and from a superficial examination it is difficult to dis- 
tinguish them from those made in the regular manner from 
crude turpentine. The acid number of such rosins is low, sam- 
ples tested by the author giving numbers between 153 and 157, 
while the unsaponinable matter may run as high, as 11. 2 per cent. 
These rosins, when crushed or cooked for size, have an unmis- 
takable odor of pine oil and this odor persists even into the 
finished paper if it is hard sized. They have been found to 
saponify rather more slowly than the regular grades and the size 
prepared from them must be boiled longer in consequence. The 
alum precipitate from such sizes has a distinct greenish color in 
comparison with the creamy white shade of that from ordinary 
size. Considering the small amount of rosin generally used in 
paper this is not a serious fault. Practical trials of such rosins 
have demonstrated that while they may give excellent results at 
times yet they are not entirely reliable. 

The method of making rosin size varies more or less with dif- 
ferent mills but the principle on which all are based is that of 



2 66 



SIZING 



combining the acid rosin with an alkali to render it soluble. 
Among the alkalis suggested are sodium aluminate and sodium 
silicate which are sufficiently alkaline to dissolve the rosin when 
their solutions are boiled with it. Size prepared with these 
alkalis precipitates alumina or silica on treatment with an acid 
or alum and these two substances aid in rilling the paper and 
imparting hardness and rattle. The alkali commonly used how- 
ever is soda ash which is obtainable in a high state of purity and 
which is said to give better results than caustic soda. The rela- 
tive value of these two probably depends on local conditions to 
some extent but it has been the author's experience that for equal 
weights of rosin the size made with caustic soda was much more 
efficient than the other. One very general mode of operation is 
that of boiling in an open kettle fitted with a steam coil or jacketed 
around the bottom. The rosin may be added first and when it 
has all melted the soda ash dissolved in the desired amount of 
water may be run in, little by little, or the soda ash may first be 
dissolved in the kettle and then the crushed rosin added to the 
boiling solution. The time of boiling varies in different mills 
from three to seven hours but even with very long boiling it is 
probably not possible to cause all of the soda ash to combine with 
the rosin, so that the final product generally contains both free 
rosin and uncombined soda. In one mill where 400 lbs. of soda 
ash were used for 2,000 lbs. of rosin and the boiling continued for 
about three hours the size made analyzed as follows: 



Freshly prepared 


Ready to use 


Per cent 


Per cent 


22 .O 


30-S 


"•3 


i5-9 


3° 


4-5 


3-4 


1 .2 


60.3 


47-9 



Combined rosin. 

Free rosin 

Combined soda, Na 2 
Free soda, Na 2 C0 3 . . . 
Water by difference. . 



It was formerly the general custom to use a neutral size, or one 
in which the rosin was all combined with soda, but more recent 
practice calls for one containing more or less free or uncombined 



ROSIN SIZE 267 

rosin. The amount of this free rosin varies with the manner 
in which the size is to be used; if it is added directly to the 
beater without first dissolving, the limit is about 35 per cent of 
the total rosin and it is usual to run considerably lower. If an 
emulsifying or dissolving apparatus is employed the percentage 
of free rosin may safely go as high as 45 per cent. The theoretical 
percentage of sodium carbonate required to give a neutral solu- 
tion with pure abietic acid is 17.5 but if this amount is used with 
commercial rosin the size will still contain a considerable amount 
of free rosin; hence it is quite general to use an even larger 
amount than this. With high free rosin sizes for use in emulsi- 
fying apparatus the amount of soda may go as low as seven parts 
per 100 of rosin. 

Neutral size is generally clear and dark in color while free rosin 
sizes may be clear and dark or opaque and light colored. If a 
free rosin size contains about 50 per cent of water and free soda 
is present, the size, on cooling, will separate a dark reddish-brown 
liquid containing the excess of soda and some of the coloring 
matter of the rosin. This separation is sometimes caused to take 
place by adding a little common salt to the size, the idea being to 
improve the color of the paper. It is doubtful if the gain in color 
is appreciable since this dark liquor when acidified gives a pre- 
cipitate which is only slightly grayish in color. The proportion 
of water in a size, besides affecting the separation of the black 
liquor, is also of importance because of its influence on the con- 
sistency of the size, which, at the end of the cook, should be 
sufficiently fluid to strain through a 60 mesh wire screen. It is 
occasionally found that a size is too thick and the attempt is 
made to thin it down by adding water, with the peculiar result 
that it becomes thicker instead of thinner. It is also frequently 
noticed that a size containing 30 per cent of water boils thinner 
than one with 50 per cent so that we are forced to the conclusion 
that a thick boil usually indicates too much, rather than too little, 
water. 

From time to time various substances have been proposed as 
possible additions to rosin size. Among these may be mentioned 



268 SIZING 

phenol, phenanthrene and linseed oil to cause the rosin to sapon- 
ify more readily and to give a better emulsion, and starch, glue, 
casein and horn to enhance the sizing power of the rosin. Other 
suggested materials are potato meal, albumen, tannic acid and 
stearin. 

Size is best added to the beater after the stock and filler are in 
but before the alum. Still better sizing results are said to be 
obtained by putting the size in the beater with enough water to 
carry it under the roll and allowing it to circulate before the 
stock is added. This however causes so much foaming that it 
is impractical. If the size contains less than 35 per cent of free 
rosin it may be added directly to the engine or it may first be dis- 
solved in luke-warm water. Hot water should never be used 
because it causes the free rosin to collect in lumps which make 
spots in the paper. There is probably not much to choose between 
adding directly to the beater or dissolving so far as efficiency 
of sizing goes but as the dissolved size may be strained through 
cloth it is preferable from the standpoint of cleanliness. 

With high free rosin sizes some form of emulsifier should be 
used in order that the emulsion of free rosin may be so fine that 
none will settle out. The emulsifier is practically a steam injector 
which takes the hot size and sprays it suddenly into a large body 
of cold water. This prevents the free rosin from collecting in 
flakes and gives very fine particles in suspension. Some forms 
of apparatus are so arranged that the operator can control the 
output and obtain at will either a milky suspension of com- 
paratively coarse particles or a semi-transparent, brownish one 
in which the particles may be as small as 0.002 mm. in diameter. 
The concentration of the emulsion is said to have a large influence 
on the results and the upper limit for satisfactory work is vari- 
ously given as a 2 to 3 per cent solution of rosin. The claims 
made for emulsification processes are more uniform, cheaper and 
better sizing and less dirt. In this country many mills which 
formerly added their size directly to the beater are installing 
emulsifying apparatus with very good results. 

The mere presence of rosin size in the stock does not mean 



FREE ROSIN IN SIZE 269 

that the paper will be sized; to accomplish this object the rosin 
must be precipitated on the fibre in such a way that the paper 
on drying will be water-resistant. The substances which will 
cause precipitation are acids, acid salts and salts of the alkaline 
earths and heavy metals. The precipitants which have been 
actually proposed from time to time include, sulphuric acid, 
sodium acid sulphate, carbonic acid, zinc sulphate, magnesium 
sulphate, calcium chloride, aluminum sulphate, etc. Practical 
trials have proved that while precipitation with acid will give 
fairly good sizing the results are by no means so permanent as 
when alum is used. None of the precipitants having an alka- 
line base as copper, lead, or zinc will give good results nor will 
the salts of the alkaline earths, as magnesium sulphate or calcium 
chloride even though they completely precipitate the rosin. 
Tests by Pauli, Frohberg and others have proved that magnesium 
sulphate, whether used alone or as a partial substitute for alum, 
has no value as a sizing agent and experiments carried out under 
the direction of the author have shown that calcium chloride is 
equally valueless. In practical working we are concerned only 
with alum or aluminum sulphate which is the precipitant univer- 
sally employed in rosin sizing. 

Researches by Wiirster in 1878 led him to the conclusion that 
the prime sizing agent was the free rosin thrown down by the 
alum and on the basis of these experiments much stress has been 
laid on the use of sizes high in free rosin. This question has 
never been definitely settled and there is still much difference of 
opinion as to whether the sizing agent is free rosin or aluminum 
resinate. Our experience has been that, other things being equal, 
a pound of rosin as neutral size has as much sizing power as a 
pound in the form of size containing 30 per cent of its rosin in the 
free state. This does not necessarily mean that the sizing agent 
is not free rosin, since the latter may be formed by the reaction 
with alum, but it does indicate that too much importance is 
placed on the presence of free rosin in the size. The reaction 
between rosin size and alum has been studied by Remington, 1 
1 Remington, Bowack and Davidson: J. Ind. Eng. Chem., 1911, 3, 466. 



270 SIZING 

Schwalbe, 1 Neugebauer, 2 Heuser 3 and many others with quite 
conflicting results. Even when considering the case of neutral 
size and alum alone there is marked lack of agreement and 
when the reaction takes place in the presence of cellulose still 
further complications are introduced by the absorptive power 
which the latter has for alumina and which Schwalbe claims 
may quantitatively effect the decomposition of 3 per cent of its 
weight of aluminum sulphate. The reaction between sodium 
resinate and alum is given by Heuser as follows: 

6 C 20 H 29 O 2 Na + Al 2 (S0 4 ) 3 = 3 Na 2 S0 4 + Al 2 (C 20 H 29 O 2 ) 6 . 

This is for equivalent quantities and indicates the formation 
of aluminum resinate. If an excess of alum is used free rosin is 
formed as follows: 

2 C 20 H 29 O 2 Na + H 2 + Al 2 (S0 4 ) 3 

= Na 2 S0 4 + 2 C 20 H 30 O 2 + A1 2 (S0 4 ) 2 . 

In the presence of cellulose these reactions are doubtless 
somewhat modified and it seems probable that free rosin, alu- 
minum resinate and alumina all play a part in producing the 
final result. 

The relation between the amount of alum and rosin used in 
the engine is of considerable importance. With a neutral size 
it was found that 0.202 lb. of alum (17 per cent A1 2 3 ) was 
sufficient to precipitate each pound of rosin while with a 31 
per cent free rosin size the figure found by titration was 0.201 lb. 
In actual operations these proportions are never even approxi- 
mated for if they are the paper is very slack sized which indi- 
cates the necessity of inducing secondary reactions between 
the aluminum resinate and the alum. It has been found by 
experience that the ratio of alum to rosin should not fall much 
below 1 1 : 1 if good sizing is to be expected, and this has been 
confirmed by laboratory experiments using a standard fibre 

1 Schwalbe and Robsahm : Wochbl. Papierfabr., 43, 1454. 

2 Neugebauer: Z. angew. Chem., 25, 2155. 

3 Heuser: Wochbl. Papierfabr., 44, 1312, 1394, 1517, 1583, 1688. 



AMOUNT OF ROSIN REQUIRED 



271 



furnish and an amount of size equivalent to i| per cent of rosin 
on the weight of fibre. These tests gave the following results: 



Percentage of rosin 


Percentage of alum 
(17 per cent A1 2 3 ) 


Sizing 
Ink test in seconds 


i-5 


I .O 


14 


i-5 


2 .O 


*34 


1-5 


2.5 


195 


1-5 


3° 


230 


i-5 


4.0 


228 


i-5 


6.0 


220 


6.0 


4.0 


210 


6.0 


8.0 


566 



The extent to which the alum may be reduced is also lim- 
ited by the difficulty which is caused by the stock sticking to 
the couch and presses of the paper machine. Practical trials 
on a book-paper machine showed that sticking was likely to 
take place if the ratio was dropped to 1.2 alum to 1 rosin, but 
that it ran safely if the ratio was 1.5 : 1. A safe, practical test 
for sufficiency of alum is to have the stock in the engine react 
slightly acid to litmus paper or turn alcoholic Congo red solution 
slightly brownish. 

The amount of rosin used in sizing paper varies greatly with 
the grade being made; in some it may drop as low as 0.25 per 
cent of the stock furnished while in hard sized orders it may 
amount to 2 per cent or even more. The sizing increases with 
the quantity of rosin used as is seen from the following figures, 
which were obtained by sizing a mixture of one-half soda poplar 
and one-half sulphite spruce beaten together in a standard 
manner. 



Per cent of rosin on 
fibre furnish 


Per cent of alum on 
fibre furnish 


Ink test in seconds 


O.38 

0.75 
I.50 
3.00 
6.00 


4 
4 
4 
4 
8 


12 

45 
226 
380 
566 



272 



SIZING 



The increase in sizing is not proportional to the increase in 
rosin throughout the series, the greatest gain being obtained 
when the rosin is increased from 0.75 to 1.50 per cent. 

The sizing of paper containing 18 per cent of ash, as well as 
that of the above series of tests, is illustrated in Fig. 35 which 
shows the marked difference caused by the filler. This indi- 
cates the waste of materials by using much more than 2§ per 
cent of rosin in paper which is heavily loaded. 



6 


















































































5 




























Un 


Eille 


iPa 


per 




















«-Fi 


lied 


Pap 


er 






















3 
m 1 










































a l 











































a 

CD 


















































































g 2 






















/ 




























































1 










































/ 


^ 








































/ 









































60 120 180 240 300 3G0 

Ink Test in Seconds 

Fig. 35. 



420 



480 



540 



600 



Trouble in sizing is frequently encountered in hot weather 
and particularly in engines where the stock tends to become 
heated. This is probably due to the rosin particles uniting to 
form larger masses which do not cover the fibres well. In 
such cases the size should be added to the stock as late as pos- 
sible. Water containing calcium bicarbonate, or the presence 
of calcium carbonate or calcium hydroxide in the stock, is par- 
ticularly bad for sizing, while calcium sulphate or chloride has 
practically no influence on the result. With the latter salt, 
even as much as 5 per cent on the weight of the fibre, has been 
found to be harmless though much less than this amount will 



ROSIN 



273 



completely precipitate the average amount of size used. This 
is probably to be explained on the assumption that the alum 
subsequently added reacts with the calcium resinate forming 
free rosin, calcium sulphate and alumina. This is a very for- 
tunate circumstance since the bleached fibre employed often 
introduces more than enough calcium chloride from the ex- 
hausted bleach to precipitate all the size used. Other disturb- 
ing factors are the soluble matters washed into the water supply 
by heavy rains, the presence of much filler, or of acid from 
incompletely washed sulphite fibre, etc. The influence of the 
filler is well illustrated by the curve on page 291. 

The sizing process is not. completed till the web of paper has 
passed over the driers and the manner of conducting this opera- 
tion has a great influence on the results. The best conditions 
are said to be moderate steam pressure on the first drier, increas- 
ing to a maximum at about the middle of the bank and again 
decreasing toward the calenders. This warms the paper up 
gradually but permits it to reach a high temperature before 
the moisture is driven off, which has been found essential to 
good sizing. 1 If the first driers are too hot the sudden escape 
of steam opens up the pores of the paper and the sizing is 
defective, while if the paper becomes too dry before the proper 
temperature is reached the sizing is also poor. Moist heat 
seems to be a requisite of good sizing and slack sized paper 
may often be greatly improved by exposing it to steam even 
at as low a temperature as ioo° C. 

Experiments by the author on the drying of sized pulp taken 
from the first press of a paper machine gave quite different 
results from those of other observers. The drier was a sta- 
tionary cylinder heated by steam and the sheets to be dried 
were held against its surface by a tightly stretched piece of old 
press felt. Two grades of paper were tested at various tem- 
peratures with the following results : 

1 Klemm: Wochbl. Papierfabr., 39, 1908, p. 1369. 



274 



SIZING 





Sizing: seconds for ink to penetrate 


Temperature of drier 










Sample 1 


Sample 2 


Deg. C. 






IOO 

106 


430 
480 


260 
280 


112 

119 


5io 
420 


270 
260 


131 

142 

152 


440 
420 
420 


250 
240 
240 



All these samples were held against the cylinder until steam- 
ing ceased and were then exposed to the air for twenty-four 
hours before testing for sizing. It was also demonstrated in 
these experiments that if the paper were alternately pressed 
against the cylinder and removed, as would be the case in 
passing over the driers of a paper machine, the sizing was only 
one-third to one-half as strong as though it had been held 
against the drier continuously. 

This question of the relation between the manner of drying 
and the sizing of the sheet is one on which little work has appar- 
ently been done, but it is one which must be investigated much 
more carefully before it will be possible to say that the best 
conditions for sizing are maintained. 

Defects of Rosin Sizing. It is the general opinion that the 
presence of rosin in paper causes more or less rapid deteriora- 
tion according to the amount present. Much work has been 
done in the attempt to. prove this point and to determine the 
maximum amount which it is safe to employ, but beyond the 
general conclusion that it is injurious if used in large amount 
there is little agreement between different observers. Under 
the action of oxygen rosin forms a substance having the nature 
of peroxide which then acts on cellulose forming oxycellulose 
and injuring the paper. This action is said to be more vigorous 
with the original rosin in ground wood than with that which has 
been made into size and reprecipitated. The discoloration of 
paper is also ascribed to the rosin but all attempts to devise a 



TESTING OF ROSIN AND ROSIN SIZES 275 

positive test which will show whether rosin sized papers will 
become yellow have thus far failed. Zschoke x concludes that 
wood-free paper with not over 1 per cent of rosin will not be- 
come yellow, while Klason 2 thinks that papers properly sized 
with rosin will not be injured within sixty years. 

If rosin sized paper is exposed to sunlight the sizing is de- 
stroyed and the paper becomes absorbent. This is also true 
of animal sized papers though the change is not so rapid. With 
rosin sizing this is undoubtedly due to the formation of the 
friable substance, insoluble in petroleum ether, which has been 
previously mentioned. The use of a small amount of tannin 
with the size is said to cause this change to take place much 
more slowly. 

Defective sizing may also be caused by calendering as this 
has been found to reduce the resistance to ink from 6 to 40 
per cent. Other factors which may cause defective sizing are 
too much filler, improper proportion of alum and poorly cooked 
size. These are all well-defined troubles and can be readily 
corrected but there are also defects which come from causes so 
obscure as to practically defy detection and for which little can 
be done. 

Testing of Rosin and Rosin Sizes. In testing rosin for use in 
size making one of the most important determinations is that 
of the acid number, which is the number of milligrams of caustic 
potash required to neutralize 1 gram of rosin. This is best de- 
termined by dissolving a weighed sample of the rosin in neutral 
alcohol and titrating directly with alcoholic KOH solution, us- 
ing phenolphthalein as indicator. With average American rosin 
about 164 milligrams of KOH will be required for every gram 
of rosin. This test indicates roughly the amount of alkali 
which the rosin will use up in the ordinary size-making process 
and it may be used as the basis for calculating the reduction 
in the amount of alkali which should give a size with a definite 
percentage of free rosin. 

1 Wochbl. Papierfabr., 44, 2976 and 3165. 

2 Paper Trade J., 1913, p. 46. 



276 SIZING 

The unsaponifiable matter may be determined by heating a 
sample on the steam bath for several hours with an excess of 
caustic potash solution, cooling, extracting with ether, as in the 
case of size, evaporating off the ether, drying and weighing. 
This unsaponifiable matter is soft and sticky in character and 
if present in large amount is likely to cause trouble by sticking 
at various points on the paper machine. 

The amount of material insoluble in petroleum ether should 
be determined by dissolving a weighed sample of the rosin in 
petroleum ether, separating the solution from the insoluble 
residue, washing the latter with several portions of ether, dry- 
ing and weighing. The insoluble matter has practically no 
sizing properties and it should be present in small amount only. 

In the case of rosin size containing no admixture of foreign 
material, the substances to be determined are moisture, free 
and combined rosin and free and total alkali. 

Moisture may be conveniently determined by weighing out 
2 to 3 grams of the size in a covered weighing bottle, dissolving 
in hot water, transferring to a weighed platinum dish, evapo- 
rating to dryness, drying and weighing. Total alkali may then 
be estimated in this dry sample by burning off the organic 

. N 
matter and titrating the residual mineral matter with — acid 

2 

using methyl orange as an indicator. For free alkali weigh out 

10 grams of size and dissolve in 200 c.c. of acid free absolute 

alcohol. Allow to stand at least eight to ten hours, or longer, 

if possible, and filter, washing the filter with absolute alcohol. 

When well washed pour boiling water through the filter and 

titrate the aqueous solution with — acid using methyl orange 

10 

as an indicator. 

Free rosin should be determined in a 5 to 10 gram sample. 
Dissolve in a small amount of hot water and wash into a sepa- 
ratory funnel keeping the volume of water as small as possible. 
Cool, add about 25 c.c. acid free ether, shake and allow to stand 
till the ether layer separates clear. If this does not take place 



ALUM 277 

readily it may be hastened by adding a few drops of "a strong 
solution of sodium chloride. When separation has taken place 
draw off the aqueous solution into a flask and wash the ether 
extract twice with small portions of water, adding these wash- 
ings to the solution in the flask. Transfer the ether extract to 
a small weighed dish or flask and replace the aqueous solution 
in the separatory funnel. Repeat the extraction with ether and 
add the second extract to the first in the weighed dish. Care- 
fully evaporate the ether, dry the residue at 105 C. for about 
two hours, cool and weigh as free or uncombined rosin. 
• Combined rosin may be determined in the soap solution 
remaining after the extraction of the free rosin. Add sufficient 
acid to completely free the rosin and then extract with ether as 
in the case of free rosin. For this determination it is probably 
well to extract three times with 25 c.c. of ether instead of twice 
as for free rosin. 

A useful qualitative test for size containing free rosin is car- 
ried out by stirring luke-warm water into the size, a little at a 
time, until a thin milk is produced and then pouring this into 
a large jar of cold water. If during the dissolving the rosin 
separates in lumps, or if on standing for an hour after dilution 
flakes settle to the bottom, the size is unsafe to use unless some 
sort of an emulsifier is employed. 

In addition to the tests already described, commercial sizes 
must be examined for such substances as starch, glue, casein, 
gum, dextrine, etc. All these are insoluble in alcohol and may 
therefore be looked for in the residue left on dissolving the size 
in strong alcohol. The character of this residue will generally 
give some indication as to the nature of the substances present 
and special tests may then be applied for those which are 
suspected. 1 

Alum. As already mentioned the rosin sizing process necessi- 
tates the use of some precipitant and the agent universally em- 
ployed is aluminum sulphate, or alum, as it is generally called in 
the paper industry. Alum is manufactured largely from clay and 

1 J. Marcusson: Chem. Rev. Fett. Ind., 19 14, 21, 1-3. 



278 SIZING 

bauxite by treatment with sulphuric acid. If calcined clay is 
added to sulphuric acid of 1.48 sp. gr. at 85 C. a vigorous 
reaction immediately takes place and the resulting mass after 
agitation and standing gradually solidifies. About 60 per cent 
of the alumina present in the clay is converted to sulphate. 
The product known as "alum cake" contains all the impurities 
of the clay and according to Bailey its average composition is 

Per cent 

AI2O3 (soluble) 12. 3-13. o 

Fe203 o. 1- o. 2 

SO3 (combined) 29. 5-3 1 . 8 

SO3 (free) 0.4- 1 . o 

Insoluble 20. 0-26. 5 

Alum cake is sometimes purified by lixiviation, separation of the 
clear liquid and evaporation to about 1.56 sp. gr. at 115 C, 
when on cooling it sets in solid blocks. 

The procedure with bauxite is very similar except that it is 
boiled with the acid for several hours, diluted to 1.35 sp. gr. at 
the boiling point, separated from insoluble matter, and then 
concentrated. The alum from bauxite may contain up to 0.7 
per cent, or even more, of Fe 2 3 and no entirely satisfactory 
method of freeing it from this impurity has yet been devised. 

For the preparation of pure aluminum sulphate, powdered 
bauxite is mixed with so much soda ash that for each molecule 
of AI2O3 (including Fe 2 3 ) there are present 1 to 1.2 molecules 
of Na 2 0. The mixture is then heated in a reverberatory furnace 
with frequent stirring for five hours. On lixiviating the result- 
ant mass a solution of sodium aluminate is obtained while the 
iron remains as Fe 2 3 in the insoluble residue. Passage of 
carbon dioxide through the solution, or its treatment with alu- 
mina (Bayer's process), causes the separation of alumina which 
on solution in sulphuric acid gives an alum containing only 0.01 
to 0.02 per cent of Fe 2 3 . A product containing less than 0.01 
per cent Fe 2 3 is generally called free from iron. 

In making alum zinc is sometimes added to reduce the iron 
to the ferrous state, in which condition it imparts only a slight 



ALUM 



279 



greenish color to the product. The presence of free acid also 
tends to mask the presence of iron. If the alum is basic, 0.05 
per cent of Fe 2 3 gives a yellowish color and if 0.15 per cent is 
present, the basic ferric salts color the alum as dark as bees- 
wax, while if free acid is present this amount of iron scarcely 
colors the alum at all. 

Characteristic analyses of alum are as follows : 1 



Insoluble in water. 
Alumina, A1 2 3 . . . . 

Iron, Fe 2 3 

Zinc oxide, ZnO. . . 

Soda, Na 2 

Sulphuric acid, S0 3 : 

Combined 

Free 

Water 



14.70 
0.12 



34.60 

0.40 

49-95 



°-49 

16.20 

0.06 

i-34 
36.62 



0.06 
18.81 

0.80 

0.76 



45-97 
1 .03 

45-291 3 2 -58 



45 



27 



-\S 



34 



0.18 

16.32 

o-5i 

0.67 
36.90 
45-42 



0.4 

17-4 
trace 



39-2 
43 -o 



0.16 

21.87 
0.40 



49-27 
27.46 



In interpreting the analysis of an alum it is to be noted that 
a large amount of insoluble matter indicates that the original 
raw material was not thoroughly broken down by the acid or 
that the purification was improperly conducted. Zinc precipi- 
tates its equivalent of size but it is seldom present in sufficient 
amount to have much influence on the value of the alum, while 
soda is usually due to the use of carbonate in the manufacture 
of porous alum but may also be derived from the soda used in 
the reverberatory charge. 

The presence of much iron in an alum has a deleterious effect 
on the color of the paper and probably also on its permanence, 
and its amount is therefore a matter of some importance. 
Authorities differ as to the permissible amount of iron, but the 
general opinion seems to be that for news papers the Fe 2 3 
should not exceed 1 per cent and that not over 0.05 per cent 
should be in the ferric state, for good writing or book papers 

1 Analysis of sample i from Cross and Bevan, "Text Book of Paper Making," 
samples 2, 3 and 4 from Griffin and Little, "Chemistry of Paper Making," 5^6 
and 7 from analyses by the author. 



280 SIZING 

0.2 to 0.3 per cent should be the upper limit and it should pref- 
erably be in the ferrous condition. For only the highest class 
of papers is it necessary to have less than 0.2 per cent of Fe 2 3 
and then the limit should be set at 0.01 per cent. While the 
appearance of an alum is improved by the reduction of the iron 
to the ferrous state it is probable that altogether too much 
stress is laid on this point as the processes of paper making 
permit its rapid oxidation so that the final result may be the 
same no matter what the condition of the iron originally. 

The amount of free acid in alum is of importance because of 
its possible effect- on the colors used, because it decomposes the 
size without throwing down alumina and because it increases 
the injurious effect of the alum on the beater bars and wires. 
If present in excessive amount it may even tend to weaken the 
paper as it passes over the driers. For use with gelatine in 
surface sizing alum containing free acid may cause brittleness 
of the paper and act injuriously on the metal plates used in 
printing. A small amount of free acid is probably harmless in 
most instances but it should be limited to 0.5 per cent. 

The value of an alum is generally considered to be in propor- 
tion to the amount of alumina which it contains, though this is 
no indication of its size precipitating power since impurities 
such as zinc salts and free acid also cause precipitation of the 
rosin. A neutral or slightly basic alum is also preferred to 
one containing free acid in spite of the fact that the basic alu- 
mina possesses practically no size precipitating power. A basic 
alum is characterized by the separation of alumina on dissolving 
to a dilute solution. 

The amount of alum used depends on a number of factors 
besides the amount of size employed. Hard water necessitates 
additional alum, as does also an increase in the temperature of 
the stock in the beater. The quantity to use is generally de- 
termined by experience rather than by scientific observation 
and it is always largely in excess of that necessary to precipi- 
tate the size. This excess is also essential in order to prevent 
the stock from sticking to the press-rolls, particularly in hot 



ALUM 281 

weather. A portion of the alum not required to precipitate the 
size is undoubtedly decomposed by the cellulose, resulting in a 
fixation of alumina on the fibres but that a considerable part is 
lost is proved by the presence of aluminum sulphate in the back 
water. For an engine holding 1000 lbs. of stock, the alum 
ordinarily employed in sizing would range from 12 to 30 lbs. or 
even higher for very hard sized papers. 

The method of adding the alum has some influence on the 
results obtained, it being found best to allow the size to become 
thoroughly mixed with the stock before furnishing the alum. 
Some mills, however, reverse these operations and add the 
alum first. It has been our experience that this gives somewhat 
inferior results though the difference is not very great. In some 
establishments it is also customary to add part of the alum 
before the size and the rest afterwards on the theory that any 
combination of size with lime salts will be prevented by the 
stronger reactivity of the alum. Experience has shown that 
even if sufficient calcium chloride is present to combine with 
all the size, subsequent addition of alum breaks down this com- 
bination and gives fully as good sizing as in the entire absence 
of calcium chloride. The method of divided alum is said also 
to reduce frothing and on this basis may be justified. 

If possible alum should be used in the form of a solution as 
this promotes rapid mixing with the stock. It is stated by 
Hoffman that the solution should never be used hot or stronger 
than 6° Be. The alum solutions may be readily prepared from 
either ground or ingot alum and should be stored in either wood 
or lead-lined tanks and distributed through lead or lead-lined 
pipes. In spite of the obvious advantages of distributing from 
a central dissolving station, many mills still add the ground alum 
directly to the beaters. The time of adding the alum is a com- 
promise between two factors; it should be added as early as 
possible to give plenty of time to complete its reaction with the 
size and it should be put in as late as possible to prevent action 
on the beater bars and bed plates. If bronze bars are used this 
second factor is eliminated and the alum can be added sooner. 



282 SIZING 

Testing Alum. The analysis of alum may be conveniently 
carried out according to the following scheme. 

Insoluble matter is determined by dissolving 10 grams of the 
alum in a small quantity of water and filtering at once through 
a weighed filter into a liter flask. After washing the filter 
thoroughly with hot water it is dried at 105 C. and weighed. 
The difference between this weight and the original weight in 
grams multiplied by 10 gives the percentage of insoluble matter. 

The filtrate and washings from the determination of insoluble 
matter should be made up to 1000 c.c. and thoroughly mixed; 
each 100 c.c. of this solution will then represent exactly 1 gram of 
alum. 

For the determination of total sulphuric anhydride, SO3, 100 
c.c. of the alum solution are diluted to about 300 c.c. and a few 
cubic centimeters of dilute hydrochloric acid added. The solu- 
tion is now heated to boiling and hot barium chloride solution 
added in slight excess. After digesting on the steam bath for 
several hours the precipitated BaS0 4 is filtered off, washed free 
from chlorides, dried and ignited in a platinum crucible. After 
the carbon has all burned off the crucible is cooled and its con- 
tents moistened first with a few drops of concentrated nitric 
acid and then with a drop or two of strong sulphuric acid. The 
acids are then very cautiously evaporated and the crucible 
ignited for a few minutes at a dull red heat, cooled and weighed. 
The percentage of sulphuric anhydride is obtained by multiply- 
ing the weight of precipitate in grams by 34.30. 

The total iron is best determined by a colorimetric method 
adapted from that of Stokes and Cain 1 and using a colorimeter 
in which the solutions to be compared are contained in two 
test tubes of the same diameter. For comparison with the 
alum a solution containing 0.10 gram ferrous iron per liter is 
made by dissolving 0.7026 gram ferrous ammonium sulphate 
in a liter of water. Into one of the test tubes 10 c.c. of this 
solution is put, together with 10 c.c. water, 5 c.c. sulphocyanic 
acid solution (saturated with mercuric sulphocyanate) , 0.01 

1 Stokes and Cain: J. Am. Chem. Soc, 1907, 29, 409. 



TESTING ALUM 283 

gram ammonium persulphate and 10 c.c. amyl alcohol. Into 
the other tube 0.5 c.c. of alum solution is run from a 10 c.c. 
burette and then 19.5 c.c. water, 5 c.c. sulphocyanic acid solu- 
tion, 0.01 gram ammonium persulphate and 10 c.c. of amyl 
alcohol are added. Both tubes are then thoroughly shaken 
and comparison of the colors is made in the colorimeter as soon 
as the amyl alcohol layer clears. If the color of the alum solu- 
tion is weak it is adjusted to the standard by adding alum 
solution, 0.1 c.c. at a time, and shaking well. If the alum 
tube shows too strong a color the alum solution may be added 
to the standard iron tube till the two match. By dividing 
0.00002 by the grams of alum in the alum tube (or by this 
number minus the grams added to the iron standard tube) and 
multiplying this quotient by 100, the percentage of iron in the 
alum is obtained. This percentage multiplied by 1.43 gives 
the total iron calculated as ferric oxide, Fe 2 3 . 

For the determination of alumina in the absence of zinc, 100 
c.c. of the alum solution are diluted to about 300 c.c. and treated 
with a few cubic centimeters of dilute hydrochloric acid and a 
few drops of concentrated nitric acid to oxidize the iron. The 
solution is brought to the boil, 5 c.c. ammonium chloride added 
and then ammonium hydroxide with constant stirring until the 
solution smells slightly of ammonia. After heating on the 
steam bath 5 minutes — when a faint odor of ammonia should 
still be noticeable on stirring — the solution is filtered, the pre- 
cipitate washed free from chlorides, dried, and ignited over a 
blast lamp to constant weight. This weight multiplied by 100 
gives the percentage of alumina and ferric oxide and by sub- 
tracting the percentage of the latter, already found by the 
colorimetric method, the per cent of alumina may be found. 

If zinc is absent the filtrate from the alumina precipitate may 
be used for the determination of alkalis. The solution is evapo- 
rated to dryness in a weighed platinum dish, ignited to drive off 
ammonium salts, cooled, treated with a little concentrated hydro- 
chloric acid and taken up with a little water. A few drops of 
concentrated sulphuric acid are added, and the solution evapo- 



284 SIZING 

rated as far as possible on the steam bath. The dish and con- 
tents are then carefully ignited to drive off sulphuric acid, heated 
a few moments to dull redness, cooled and weighed. The 
weight of sodium sulphate thus obtained multiplied by 43.64 
gives the percentage of sodium oxide in the alum. 

The presence of zinc in an alum renders the above procedure 
for alumina inaccurate and a qualitative test for zinc should 
therefore be made before proceeding with the alumina deter- 
mination. To a moderately strong solution of the alum add 
an excess of ammonia, heat to boiling and filter. To the clear 
filtrate add a few drops of ammonium sulphide and heat to boil- 
ing. If zinc is present a flocculent white precipitate will form 
which on boiling a few minutes will settle rapidly. 

In the presence of zinc the alumina and iron should be deter- 
mined by the basic acetate method. Dilute 100 c.c. of the alum 
solution to 500 c.c, add 2 grams of sodium acetate and a few 
drops of acetic acid. Bring to a boil and keep in active ebulli- 
tion for ten to fifteen minutes. Allow to settle, decant the clear 
liquid through a filter as rapidly as possible and boil up the 
precipitate with water. Repeat the settling, decantation and 
boiling twice more and finally wash the precipitate on the filter 
with hot water containing a little ammonium acetate. The 
filtrate and washings are evaporated to 200 c.c. and if any pre- 
cipitate separates it should be filtered off, washed and united 
with the rest of the precipitate which is then to be dried, ignited 
and weighed as above described for alumina. This method 
also gives the alumina and ferric oxide together and from the 
total weight that already found for ferric oxide should be 
deducted in order to give the alumina. 

In the filtrate from the basic acetate precipitate the zinc may 
be determined by neutralizing as nearly as possible with ammonia, 
heating to boiling and adding ammonium sulphide drop by drop 
so long as a precipitate continues to form. The boiling is con- 
tinued fifteen or twenty minutes, the zinc sulphide allowed to 
settle and the clear liquor tested with ammonium sulphide to 
make sure that precipitation is complete. If such is the case 



TESTING ALUM 285 

filter off the zinc sulphide, wash with hot water and dry the filter 
in the oven. Remove the precipitate from the filter, burn the 
latter over a porcelain crucible, add the zinc sulphide and ignite 
with free access of air, gently at first but finally as strongly as 
possible. The occasional addition of a small piece of ammonium 
carbonate aids the operation and the ignition should be continued 
until on cooling and weighing a constant weight is attained. This 
weight multiplied by 100 gives the percentage of zinc oxide in 
the alum. 

The presence of free acid in alum is indicated by a blue color 
with Congo red solution; if free acid is absent a dirty brown 
color only results. Craig 1 has proposed a method for the direct 
determination of free acid in alum. The solutions required are: 
(1) Potassium fluoride prepared by dissolving the pure salt in 
distilled water to a specific gravity of 1.45, neutralizing if neces- 
sary with caustic potash or sulphuric acid until 1 c.c. in 10 c.c. of 
distilled water shows a faint pink with phenolphthalein, filtering 
and diluting the clear solution to a specific gravity of 1.35. This 
solution should be preserved in glass coated with wax. (2) Sul- 
phuric acid standardized against sodium carbonate using methyl 
orange as an indicator. (3) Caustic potash, free from alumina 
and similar bases, standardized against the acid, with phenol- 
phthalein, in about 40 c.c. of water to which 10 c.c. of the potas- 
sium fluoride solution have been added. In making the test 
a weighed portion of the alum is dissolved to give a solution of 
1 to 3 grams of alumina in 200 c.c. ; this is filtered and 20 c.c. are 
gradually added, with stirring, to 10 c.c. of the potassium fluoride 
solution, to which 50 to 60 c.c. of distilled water and 0.5 c.c. of 
0.2 per cent solution of phenolphthalein have been added. When 
free acid is present the mixture is practically colorless and stand- 
ard alkali is slowly added until a faint permanent pink color is 
obtained; the amount of alkali required is calculated to free 
acid. 

Moisture in alum cannot be determined by direct drying or 

1 J. Soc. Chem. Ind., 1911, 30, 184. 



286 SIZING 

ignition; it is generally estimated by deducting the sum of the 
determined substances from ioo and calling this difference mois- 
ture. Griffin and Little x recommend the following method: 
Ignite a weighed sample of alum in a platinum crucible until copi- 
ous fumes of S0 3 appear, cool, weigh and note the loss. Treat 
the ignited sample with hot hydrochloric acid until all lumps are 
broken down, filter, and wash the residue with hot water. The 
filtrate and washings are precipitated with barium chloride and 
the sulphuric acid determined as usual. The percentage of SO3 
here found, deducted from the total (determined in a separate 
sample), gives the percentage driven off by ignition and this 
taken from the total loss on ignition, in per cents, leaves the 
percentage of moisture in the sample. 

The size precipitating power of an alum may be ascertained if 
desired by titrating a standard size solution by one of the alum 
in question. This test gives the total precipitating power of 
the alum and makes no distinction between sulphates of alumina, 
iron, or other bases or of free acid. It consequently shows little 
as to the value of an alum and its .usefulness is still further reduced 
by the fact, already mentioned, that a considerable excess of 
alum over the theoretical must always be used. 

Casein Sizing. Casein, as an engine size, imparts firmness, 
elasticity and strength to the paper and enables it to take a good 
finish. It aids in keeping down the fuzz on the surface of the 
paper and for this reason may form a partial substitute for beat- 
ing. It does not size the paper in the same sense that rosin does 
as the precipitated casein is not water repellent. 

Casein being an insoluble body must first be brought into 
solution by treating with an alkali, after which the solution may 
be incorporated with the rosin size or it may be added directly to 
the beater. In either case the addition of alum to the stock 
causes the precipitation of a bulky, gelatinous mass which 
adheres to the fibres and upon drying with them aids in filling 
the pores. Owing to the nature of the precipitated casein prac- 
tically all of it is retained by the paper and when as little as 2 per 

1 Chemistry of Paper Making, p. 382. 



VISCOSE 287 

cent is added to the stock its presence is readily detected in the 
finished sheet. 

Unless used with considerable care casein is apt to impart an 
unpleasant odor to the paper. If used in too large proportions it 
cements the fibres together so firmly that the folding and tearing 
strength of the paper is considerably reduced though at the same 
time the bursting and tensile strength is increased. Probably 
from 2 to 3 per cent is the maximum which can be used without 
making the paper brittle. Because of these drawbacks, and also 
because of the comparatively high cost of the material, casein 
sizing is not generally employed and may be said to be used only 
for special purposes. 

Glue. Glue has been exploited as an engine size in much the 
same way as casein and for the same reasons. Unlike casein, how- 
ever, it requires only hot water for its solution and it is not pre- 
cipitated by alum. For this reason its retention is very low, 
being probably only that amount which clings to the surface of 
the fibres from the very dilute solution in the beater. Its low 
retention was proved in one experiment where 2 per cent was 
added to the stock in the beater and yet the paper made from 
it failed to show its presence when tested by all ordinary 
methods. 

It is asserted by many of the older paper makers that by the 
use of glue in the beater they can obtain results which they can 
get in no other way. Its use is, however, costly and its effects are 
probably greatly over-rated. 

Viscose. This material, which is a solution of cellulose pre- 
pared by means of caustic soda and carbon bisulphide, was at 
one time proposed for engine sizing. The solution was added to 
the beater and the cellulose regenerated by the subsequent addi- 
tion of magnesium sulphate or alum. Theoretically the sizing 
of a paper by rilling its pores with a substance of the same chemi- 
cal composition as the fibres composing the sheet is a very attrac- 
tive proposition. Practically, however, the process has never 
attained any wide application, probably because of the some- 
what complicated nature of the chemical reactions; because it 



288 SIZING 

charges the engine with certain undesirable chemicals; and 
because of its cost. 

This process also does not size by making water resistant, as 
does rosin, but its action is more in the nature of the starch sizing 
of textile goods. 

Rubber Resins. These resins which are obtained as a by 
product from the treatment of certain grades of rubber have been 
suggested as of possible use in sizing paper. As they are unsa- 
ponifiable they cannot be dissolved in alkaline solutions and hence 
can only be used to replace the free rosin in the size. By this 
means they are dissolved and held in suspension and thus may 
be added to the beater just as is ordinary size. Experiments in 
German mills have indicated that this material has very little 
value but our own tests give contrary results and seem to 
show that it has more sizing value than an equal amount of 
colophony. 

If this material ever comes on the market in sufficient quan- 
tity to compete in price with rosin it is certainly worthy of further 
investigation. 

The Mitscherlich Sizing Process. Among the substances 
occurring in waste sulphite liquor are compounds derived from 
the wood which are sufficiently like tannic acid to possess its 
power of precipitating gelatine. This property has been utilized 
by Dr. Mitscherlich as the basis for an engine sizing process 
which is conducted as follows : Ordinary glue is digested at 6o° C. 
with about ten times its weight of waste sulphite liquor. After 
several hours, during which time the mixture should be stirred 
occasionally, the glue is dissolved and the solution is then diluted 
with more waste liquor until it is present to the extent of fifty 
times the weight of the glue. This dilution should be conducted 
at ordinary room temperatures and should be made very grad- 
ually and with constant stirring. The whole is allowed to stand 
for twenty-four hours to allow the flocculent precipitate to settle, 
the clear liquor is then decanted and the precipitate diluted with 
a quantity of water equal to about fifty times the weight of the 
original glue. A little alkali is next added to neutralize the free 



THE MITSCHERLICH SIZING PROCESS 289 

acid and to dissolve the compound of glue and astringent material 
and the solution so prepared is then ready to add to the engine. 
Alum, or an acid, causes the re-precipitation of the flocculent 
gelatine compound which adheres to the fibres and imparts to 
them its sizing properties. This process has never met with 
very wide application. 



CHAPTER X 
LOADING AND FILLING MATERIALS 

Nearly all classes of papers, except a few for special purposes, 
contain some mineral filling or loading material and unless it is 
used to an excessive extent it cannot be considered an adulterant. 
In fact without some filler it is impossible to produce many of 
the grades which modern printing practices demand, since it fills 
up the interstices between the fibres and gives a better surface 
for process cuts and half-tones which are so largely used. It also 
makes the paper more opaque, improves the feel, and enables 
it to take a better finish on calendering, all of which are of 
importance to the trade. 

Fillers tend to increase the weight more than the bulk of the 
paper and therefore cannot be largely used in light, bulky papers 
such as the so-called "featherweights." On the other hand, 
when they are used in very large amounts, and the paper subjected 
to supercalendering, they are of great assistance in producing 
the effects desired in imitation coated papers. When a filler is 
used in large amount it quite seriously reduces the strength of 
the paper produced; hence when the strength of a paper is 
specified, and a filler is used, a better grade of fibrous stock must 
be employed and more care used in manufacturing than if no 
filler were used. This has been amply demonstrated in Ger- 
many where in 1904, at the instigation of the Royal Testing 
Office, the restrictions as to amount of ash in the various classes 
of papers were abolished. Since that time it has been found that 
the requirements for strength have sufficed to keep the percentage 
of ash very largely within the limits formerly prescribed. The 
amount of filler also has a notable effect on the sizing, for as the 
percentage of ash in the paper rises the sizing, as shown by the 

290 



LOADING AND FILLING MATERIALS 



291 



time required for writing ink to penetrate the paper, decreases. 
This is well illustrated by the curves in Fig. 36, which show 
the percentage of ash and the sizing tests on a large number of 
samples taken from the same run of paper. 

The materials commonly used as fillers are china clay, talc, 
asbestine, calcium sulphate in its various forms, heavy spar, 

































































20 

100 


































































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£ 60 t 












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Roll Nos. 



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25 



30 



Fig. 36. Effect of Filler on Sizing 

blanc fixe and. precipitated chalk. Many of these are sold under 
trade or fancy names and frequently at prices which do not 
correspond to their actual value. In addition to these, certain 
colors, as ochre, lead chromate, ultramarine, etc., are sometimes 
used in sufficient quantity to affect the bulk and ash of the paper, 
but as these are used primarily for coloring, and their loading 
effect is merely incidental, they will not be considered here. 



292 LOADING AND FILLING MATERIALS 

The qualities to be considered in judging a filler are color, 
fineness, absence of grit, mica, etc., solubility, specific gravity and 
chemical composition. The chemical analysis of a filler, as a 
means of checking individual shipments of the same material, 
is of little value, except in special cases where for some reason a 
certain constituent must be proved absent, or else present in 
definite amount. It is essential, however, to know the chemical 
composition of the various fillers, as this makes it possible to tell 
from the analysis of a paper ash what kind of filler was used, and 
it is also necessary if it is desired to know the amount of filler in 
the paper, as many fillers, on igniting the paper to an ash, lose 
water which would normally be retained by them in the finished 
paper. The specific gravity is of importance, as it shows how 
the filler will affect the bulk of the paper, while the presence of 
grit in any considerable amount indicates that the wires, felts 
and jackets will be subjected to unnecessary wear and that the 
paper may be defective to such an extent as to cause serious 
trouble in printing. When making heavily colored papers in 
which soluble dyes are used, the type of filler should be selected 
only after consideration of the dye to be used, for different fillers 
have different absorptive capacities for the various dyes. Proper 
selection of the filler will therefore be of considerable assistance 
in obtaining satisfactory absorption of the dye and in reducing 
its loss. The relation of fillers to dyes will be discussed in 
Chapter XL 

The proportion of the filler added to the engine which appears 
in the finished paper is spoken of as the retention. This may 
vary from 30 to 90 per cent, though the latter figure is only 
reached under very exceptional circumstances and a retention of 
50 per cent is generally considered satisfactory. Many factors, 
other than the filler, influence its retention and it is impossible 
to estimate their effects, except in a general way. The kind of 
stock and the extent of its beating, the speed of the paper machine, 
the pull on the suction boxes, the amount of filler added and 
the thickness of the sheet must all be taken into consideration. 
Slow or " greasy" stock, a light suction and a thick sheet all 



RETENTION OF FILLERS 



293 



tend to give high retention, while in the case of sulphate of cal- 
cium the retention increases with the amount added. 

A study of the loss of filler taking place at different parts of 
the paper machine was made in a German mill x during the 
running of a rotary press print paper of 50 grams per square 
meter, made from stock containing 25 per cent sulphite and 75 per 
cent ground wood. The ash in the air dry stock at various 
points was as follows: 

Per cent 

Stock from the chest 20. o 

Stock just before suction boxes 19.0 

Stock after the couch 15.0 

Stock after first press 14. o 

Stock after second press 13.5 

Finished paper 13-0 

The apparently slight loss in the drainage through the wire is 
due to the fact that the white water was used over again and the 
ash in the stock actually flowing onto the wire would therefore 
be greater than that in the chest. 

Working with sulphite, and with sulphite and soda furnishes, 
Kress and McNaughton 2 found the retention to decrease slightly 
as the amount of clay added was increased. This is contra- 
dictory to the results given in the subjoined table from observa- 
tions by the author. They also found, as would be expected, 
that increasing the thickness of the sheet — or the ream weight — 
increased the retention. It was also increased as the amounts of 
size and alum were increased, and by greater hydration of the 
stock in the beater. 

The following figures from tests made under the observation of 
the author show what may be expected from various fillers when 
used in manufacturing high grade book papers. 

1 Paper: 1916, Sept. 20, p. 13, from Wochbl. Papierfabr. 

2 Kress and McNaughton: Paper, Oct. 3, 1917. 



294 



LOADING AND FILLING MATERIALS 



Filler 


Percentage in finished 
paper 


Percentage retention 


China clay 


39-1 
32.2 
26.7 
25.6 

i5-i 
24.8 
19. 1 
12 .0 

9-7 
22.3 
10.8 
10.2 
24.9 
24.2 
27.9 


76.2 
74.6 
68 6 




n it 


n n 


66.5 
57-6 
38.7 
40.9 
36.6 
54 -o 
72.4 
46.1 

S2.4 
64.4 

51-2 

39 -o 


11 ii 


Precipitated chalk 




ii ii 


ii ii 


Asbestine 




" 


Pearl finish 


Crown filler 


Blanc fixe 





Clay. Clay is a soft, friable, sectile, white substance showing 
irregularly shaped particles under the microscope and possessing 
only a moderate plasticity when mixed with water. It is a 
mixture of hydrated silicates of alumina containing particles of 
quartz, mica and felspar and its chemical composition is approx- 
imately Al203-2Si02'2H 2 0. It is formed by the weathering 
of felspathic minerals and the presence of mica indicates its 
granitic origin. Those clays which remain overlying the rock 
from which they were formed are known as residual, while those 
which have been conveyed to a distance by eroding influences 
are called sedimentary. The former are usually more free from 
iron and of better color than the latter. Good grades of clay 
are found in England, France, Bohemia and the United States, 
but in spite of our own deposits the greater part of that used in 
this country is still imported. This is probably due in large part 
to insufficient care or improper methods of preparation, and it is 
thought that these will shortly be overcome so that domestic 
clays will play a much more important part in American manu- 
facture. 

Clay is prepared for the market by washing it with a stream 
of water through long sluices of riffles, in which the sand and 
mica are caught, into tanks or basins in which the fine clay is 



CLAY 



295 



allowed to settle. The water is then drawn off and the clay dug 
out and dried when it is ready for market. Instead of these 
crude methods the fine clay and water is sometimes passed 
through filter presses, and there has recently been proposed an 
electrolytic method of purification and separation which is 
claimed to give a product perfectly free from grit and much 
dryer than that from any filter press. Even the very finest 
washed clays contain a small proportion of sand and mica and 
there is always some moisture present. For English clays up to 
12 per cent is permissible though it more frequently runs under 
than over that figure. It is not well to have a clay too dry as it 
causes loss in handling and the dust is bad from a hygienic 
standpoint. Freezing moist clay causes no permanent change 
in composition or physical properties so that clay which has 
been frozen can be used with perfect safety after it has been 
thawed out. 

The following analyses give a good idea of the composition of 
different grades of clays; numbers one to four being English clays 
tested by Remington x while five and six are American clays. 



No. of clay 


1 


2 


3 


4 


5 


6 




Coatings 


High 
grade 
papers 


News 


White 
printings 












Silica, Si02 

Alumina, AI2O3 

Ferric oxide, Fe 2 03. . . 

Lime, CaO 

Magnesia, MgO 

Alkalis, K 2 


46.21 

39.82 

O.38 

0-45 
O.IO 

0.23 
12.81 


47.60 
38.26 

0.55 
O.42 

0.20 

0.57 
12 .40 


46.46 
37-40 
2.00 
0.86 
0.21 
1 .26 
II. 81 


45-92 
38.43 
0.71 
1. 18 
0.21 
0.78 
12.77 


45-67 

37.86 

I.48 

O.05 

O.OI 

0.80 
13.22 


43-36 
40.54 
O.90 
0.08 
0.38 
0.88 


Total water 


13-86 




Grit per cent 


100.00 
0.09 


IOO.OO 
O.32 


100.00 

2.22 


100.00 

2.28 


99-09 


100.00 







The similarity of these analyses is quite noteworthy and it is 
evident that, apart from the ferric oxide which seriously influences 



J. Ind. Eng. Chem., 3, 555. 



296 



LOADING AND FILLING MATERIALS 



the color, the qualities by which a clay may be judged are largely 
physical. It is stated by one authority that if the grit rises over 
2 per cent the clay would be objectionable for high grade news- 
paper. 

The total water in these clays is very largely that chemically 
combined. This is not driven off on drying at ioo° C. but is 
expelled at a red heat or at the temperature of the usual ash 
determination. For this reason the percentage of ash as deter- 
mined in a paper loaded with clay should be divided by 0.88 in 
order to convert the ash into the approximate amount of actual 
filler; this is neglecting the ash from the fibrous materials and 
from the size and alum which is usually insignificant in compar- 
ison with the filler. Clay loses all hygroscopic moisture at 
ioo° C. and all combined water at about 500 C. Clay which 
has been dried at ioo° regains its plasticity on soaking in water. 
In this connection it should be noted that some air dry clays 
contain a small amount of moisture which is driven off on drying 
at ioo° C. and again absorbed on exposure to the atmosphere. 
In a number of high grade clays this moisture was found to 
amount to 0.43 to 0.77 per cent of the weight of the air dry 
clay. 

The size of particles varies greatly in different clays and the 
proportion of coarse and fine particles may be quite different in 
clays which are very similar in appearance. Tests of a number 
of clays by separation of the particles which settle if ins. in 
different lengths of time gave the following results: 



Settling in 1 minute 

" " 1-10 minutes 
" " 10-120 " 
" " over 2 hours. . 



Domestic 


UXL 


GAC 


GH 


Per cent 


Per cent 


Percent 


Percent 


2 


4 


26 


13 


20 


24 


IO 


35 


3° 


37 


28 


25 


48 


35 


36 


27 



AR 



Percent 

44 
25 
12 

19 



In the case of UXL clay the sizes of the particles separated in 
this way were found to be 









m 



•v.A'' =' *-.,, 1 '. i {> «t ."''■** •',;•%«."'' .•^.'•4 '>.v- f.'i 





*§^%' v #^ 




Plate 27 

Domestic Filler Clay. Magnification 100 diameters. Photographed by 

Bureau of Standards. 







?'%£? . "T" 






i^fe 



"i * ' X 



sr . ;; " ft* 






w 




> 



Plate 28 

English Coating Clay. Magnification 100 diameters. Photographed by 

Bureau of Standards. 



CLAY 297 

Settling in 1 minute o. 028 m.m. 

1-10 minutes o. 007-0. 018 m.m. 

10-120 minutes o. 0035-0. 007 m.m. 

over 2 hours o. 0015 m.m. 

The specific gravity of clay is variously given as 2 to 2.86. 
Observations by the author on six different samples of thoroughly 
dried English clays showed them to range from 2.568 to 2.634. 
The weight per cubic foot of clay as ordinarily received varies 
according to the method of handling from 53 lbs. when the fine 
material is run in loosely to 84 lbs. when the clay is tamped in 
hard. This is for clay with about 7.5 per cent of moisture. 

Clay is usually added to the stock in the beater soon after it is 
furnished so that it may be well distributed before the alum is 
added. The old way was to add the dry clay direct to the 
beater but the more progressive mills are now mixing the clay 
with water and straining before adding to the stock, thus avoid- 
ing much dirt. In preparing domestic clays for use in this way 
a little ammonia or sodium phosphate is sometimes found to be 
of great assistance in helping the clay to work up and in keeping 
it in suspension. In testing this clay mixture for uniformity 
it should be noted that the consistency of a clay-water mixture 
is dependent on the physical qualities of the clay as well as upon 
the amount used. Of six clays which were mixed in such a 
way that 100 c.c. of the mixture contained from 19.6 to 19.9 
grams of dry clay the Baume readings varied from 16. 5 to 23 
showing that this method cannot be used for daily control if the 
clay supply varies. 

A satisfactory control test for the clay mixture supplied to 
the beaters may be made by determining the weight of a definite 
volume of the mixture in comparison with an equal volume of 
water. A 250 c.c, glass stoppered, ungraduated flask is a con- 
venient volume to use. First clean, dry and weigh the empty 
flask including the stopper; then fill it completely with distilled 
water, insert the stopper carefully so that no air is trapped, dry 
the outside of the flask and weigh again. Once these two 
weights are established for a given flask they may be consid- 



298 LOADING AND FILLING MATERIAL 

ered as constants. The test therefore consists simply in filling 
the flask with the clay mixture, cleaning the outside, especially 
around the stopper, and weighing. 

Assuming the specific gravity of clay to be 2.6 the calculation 
of the weight of dry clay in the flask would be as follows: 

Let x = weight of dry clay in flask 
y = weight of water in flask 
w = weight in grams of flask full of clay mixture 
c = capacity of flask in cubic centimeters = weight of 

water it will hold 
/ = weight of empty flask in grams. 

Then x = w —f — y 

x 

y =c ~77 
2.0 

X = w — / — c -\ 

2.0 

_ 2.6 (w —f) — 2.6 c . 
1:6 

X = I.625 w ~ I -^> 2 5 (/ + c). 

Since / and c are constants it is only necessary to make a 
single weighing of the flask full of clay mixture in order to be 
able to calculate the amount of dry clay it contains. This can 
be converted readily into pounds per inch in any measuring 
tank which may be used. 

This method of testing has been employed in mill control 
work for a number of years and if the flask is weighed to a tenth 
of a gram the results are found to check closely with those ob- 
tained by drying and weighing a definite volume of the clay 
mixture. 

Gypsum. This is a natural calcium sulphate, CaS0 4 • 2 H 2 0, 
and is prepared for use as a filler by grinding, or it may be cal- 
cined, finely ground, washed and dried quickly to prevent its 
reabsorbing water and becoming hard and compact. The ground, 



PEARL HARDENING 299 

uncalcined mineral has the form of plates. Three-quarters of 
the water of crystallization of gypsum is driven off at a tem- 
perature of 120 C. and the calcined gypsum which is formed 
takes up water readily and sets to a firm mass. If, however, 
the gypsum is heated to over 160 C. there is formed an an- 
hydride which absorbs water very slowly and hence may be 
rapidly washed. This anhydride on long soaking in water 
changes in form from the irregular particles of the ground 
mineral to small needle-shaped crystals. This change takes 
place so slowly that it is doubtful if it is completed during the 
time elapsing between the furnishing of the engine and the 
running of the stock into paper. 

Gypsum is generally added directly to the beating engine and 
results in the production of rather soft paper. Its use also tends 
to fill up the felts due to the crystallization of CaS0 4 • 2H2O. 
All gypsum is soluble in hydrochloric acid, or in 400 to 500 
parts of water, which causes serious loss and poor retention 
unless the back-water is used over again. This solubility has 
not been found to interfere in any way with the rosin sizing in 
the engine in which it is used and in certain cases it is even 
claimed to be beneficial. The loss on ignition of calcined gyp- 
sum is only 0.5 to 2 per cent, while that of the uncalcined mate- 
rial is nearly 21 per cent. 

Pearl Hardening is an artificial, hydrated calcium sulphate 
made by precipitating a solution of calcium chloride with sodium 
sulphate. It may occur in two forms, flat, tabular crystals or 
minute, needle-shaped crystals. Its specific gravity is 2.39 and 
it loses 21 per cent of its weight on ignition. Other names 
for calcium sulphate preparations, either hydrated or anhy- 
drous, are Pearl White, Crown Filler, Pearl Finish, Annaline, 
Alabastine, etc. Some of these contain considerable water be- 
sides that chemically combined, and extravagant claims are fre- 
quently made as to their advantages both as to the finish 
imparted to the paper and the amount retained. These claims 
are to be taken with a grain of salt as all possess essentially the 
properties of gypsum or pearl hardening. 



300 LOADING AND FILLING MATERIALS 

Precipitated Chalk or calcium carbonate is occasionally used 
as a filler particularly in very thin papers of the Bible class such 
as are now used so largely for the printing of dictionaries and 
encyclopaedias. It may be added directly to the engine but 
much better results are obtained by mixing a solution of cal- 
cium chloride with the stock and, when it has become thoroughly 
incorporated, precipitating it with a solution of sodium car- 
bonate. Care should be taken that the quantities used are 
approximately equivalent as otherwise serious losses may occur; 
a slight excess of either one has not, however, been found to be 
injurious to the paper though a large excess of calcium chloride 
would cause it to absorb moisture and become limp and lifeless. 

Calcium carbonate seriously interferes with the rosin sizing 
and even when the size is precipitated by alum before the filler 
is added it has been found practically impossible to produce a 
well-sized sheet. The advantage of precipitated chalk lies 
largely in its color since it imparts to the paper a much whiter 
color than can be obtained by the use of clay. It also gives 
the paper a characteristic velvety feel though it does not take 
such a high polish on supercalendering as does a clay-filled 
paper. 

Talc. Talcum or Spanish chalk is a hydrated silicate of 
magnesium. A part of the magnesia is nearly always replaced 
by alumina so that it may be regarded as a double silicate of 
magnesium and aluminum with the magnesium largely in ex- 
cess. It is very soft, has a characteristic soapy or greasy feel 
and is usually of a creamy or greenish white shade. Its specific 
gravity is 2.6 to 2.9. It is very resistant to acids and solutions 
of alkalis and also to heat, losing no water below a red heat. 
In preparing it for the market the stone is sorted according to 
color and then ground and graded either by an air blast or by 
bolting. The product is not so fine as clay and the grit is usu- 
ally greater. It is often adulterated with heavy spar or more 
often with ground limestone. 

Talc improves the printing qualities and the feel of the paper 
and gives it a rag-like appearance. It is said that 20 per cent 




Plate 29 

Crown Filler. Magnification 100 diameters. Photographed by 

Bureau of Standards. 




Plate 30 

Talc. Magnification 100 diameters. Photographed by 

Bureau of Standards. 




Plate 31 
Asbestine. Magnification joo diameters. Photographed by 
Bureau of Standards. 



HEAVY SPAR AND WITHERITE 



301 



of talc will give the same results as 30 to 40 per cent of lower 
grade china clay. 

Asbestine, or agalite, is a fibrous talc which occurs as an alter- 
ation product of tremolite. It is of American origin and is ex- 
tensively prepared in St. Lawrence County, N. Y. It is nearly 
pure (95 to 97 per cent) magnesium silicate and being in the 
form of rodlets attaches itself well to the fibres and gives good 
retention. It does not impart quite so high a finish to the 
paper as does talc. The best grades are free from sand, nearly 
free from iron and almost snow white. This material loses 
up to 1.3 per cent on drying at ioo° C. and from 0.5 to 7 per cent 
on ignition. The following analyses are fairly representative of 
the composition of asbestine or agalite. 





1 


2 


3 


Silica, SiC>2 


60.59 
0.13 
0.23 
1. 16 


61.89 
1.36 
0.44 




Alumina, AI2O3 

Ferric oxide, Fe203 


O.31 
O. IO 


Manganese oxide, MnO 

Calcium oxide, CaO 




4.21 

30.70 

1 .40 

100.00 




Magnesia, MgO 

Water 


34-72 

3-77 

100.60 


32.12 

4-3° 

98.84 





Heavy Spar and Witherite are sometimes used as fillers. The 
former is a naturally occurring barium sulphate, BaS0 4 , while 
the latter is carbonate of barium, BaC0 3 . In preparing the 
heavy spar the foreign stone is broken off and the spar is first 
ground dry, then wet and finally washed. 

Neither of these materials is very satisfactory as their high 
specific gravity, 4.2 to 4.5, causes much loss of filler and also 
settling on the wire so that the two sides of the sheet are not 
alike and the wire side is particularly destructive to pens and 
type. If barium sulphate is to be used as a filler it should be 
precipitated in the engine by adding first barium chloride and 
then a solution of sodium sulphate and great care should be 
exercised that loss does not occur through an insufficiency of 
the latter. 



3° 2 



LOADING AND FILLING MATERIAL 



Testing Fillers. The color of fillers is best determined by- 
comparison with standard samples of similar materials. As the 
moisture present has a very great influence on the color, espe- 
cially with clays, the materials compared should be equally 
dry. This is readily assured by drying at ioo° C. before 
comparing. One method, which is extensively used, is to mix 
the material to a paste with water on a glass plate and after 
drying to compare with the standard, similarly treated. A bet- 
ter method and one which can be rapidly carried out is to use a 
block of wood in the top of which there are shallow compart- 
ments separated by knife edges 
coming flush with the upper sur- 
face of the block. Such a test- 
ing block is shown in Fig. 37. 
Into one of these compartments 
the standard material is pressed 
by means of a polished steel 
spatula and in the next the filler 
to be compared is placed. The 
knife edges permit of very close 
contact of the two samples, the 
polished spatula gives a good 
surface and the small size of the block allows it to be easily 
handled so that it may be held in any position with regard to 
the light and the samples examined from all sides. 

In many cases it is well to note how much a filler can be im- 
proved by the addition of blue. This may be readily done by 
grinding the dry filler in a mortar with a very little ultramarine 
and then comparing the color with the same material unblued 
or with the standard. 

To determine whether a clay has been blued, it may be moist- 
ened with turpentine to form a rather thin paste on a porcelain 
plate, and then compared with samples which are known to be 
blued and unblued and which have been treated in the same 
manner. The artificially colored clays are said to give a bluish 
green color but as it is claimed there are a number of natural 




Fig. 37. 



Block for Testing Color 
of Clays 



TESTING FILLERS 303 

English clays which give this same color with turpentine the 
test cannot be considered as conclusive. 

A better method is carried out as follows: In one of two 
similar white porcelain dishes place a measured amount of 
freshly prepared saturated lime water and in the other dish an 
equal amount of distilled water. Then into each of these liquids 
dust, from the end of a knife or spatula, a little at a time, equal 
amounts of the clay. After allowing to stand for a few minutes 
the excess liquid should be siphoned off and the moist clay 
examined. If the clay has been artificially blued the lime water 
will remove the bluing so that the two samples will appear 
quite different after this treatment. Although neither of these 
tests is entirely satisfactory, yet if both are applied it is possible 
to get a fairly accurate idea whether the sample has been arti- 
ficially blued or not. 

The grit in clay or other loading material may be determined 
in a number of ways. One roughly quantitative test is to place 
a little of the clay in the mouth when the grit may be readily 
detected between the teeth. A more accurate procedure and 
one which may be easily duplicated by independent operators 
is to weigh out a sample of the clay, place it on a standard mesh 
screen and wash it with a spray of water until the water running 
away is perfectly clear. The residue on the screen is then 
dried, weighed, and reported as grit. The size of the sample 
may be varied according to the preference of the operator but 
20 grams has been found to be a convenient amount. Some 
form of spray head which delivers a fine spray under a consid- 
erable pressure will be found very satisfactory for washing the 
clay on the screen. It is also desirable to make the test on 
both 200-mesh and 300-mesh screens in order to get a more 
comprehensive idea of the character of the grit. 

A flotation process which gives excellent comparative results 
may be carried out by means of a large, wide mouthed, bottle 
fitted with an inlet tube for water and a siphon whose inlet is 
always kept near the surface of the liquid by means of a float. 
This siphon is fitted with an automatic stop to prevent its en- 



3°4 



LOADING AND FILLING MATERIALS 



tirely emptying the bottle. The clay, or other filler to be 
tested, is mixed with water and placed in the bottle and water 
is forced in rapidly through the inlet tube until it rises to a 
mark near the neck. The mixture is allowed to stand a definite 
time and the siphon then started; this process is repeated until 
at the end of the settling period the water is perfectly clear for a 
definite distance down from the filling mark. Any material 
settling more than this distance in the standard time is con- 
sidered as grit and its quantity is determined by drying and 
weighing. It is evident that the dimensions of this apparatus 



Tube Support 



\ Siphon Tube-H 



Hose 
Connection — »■ 




1 -tWater Inlet 
\ Li£ Rubber Hose 

\~ 

Glass Receptacle 



Graduations 
2" apart 



Fig. 38. Apparatus for Determining Grit in Fillers 



may be arranged to suit the convenience of the operator but 
those of an outfit which gives very satisfactory results with 
clay, blanc fixe, asbestine, etc., are shown on the accompanying 
sketch, Fig. 38. This method cannot be employed with calcium 
sulphate because of its slight solubility. 

The grit, when separated by any method, should be examined 
by means of the microscope as its appearance reveals much as 
to the quality of the filler and gives some idea of the trouble 
it is apt to cause. Thus the grit from clay may be either sand 
or mica, and, while the former causes wear on the wire and some- 
times pinholes in the paper, the latter may make shiny spots 



TESTING FILLERS 305 

which are apparent on looking across the sheet and also give 
trouble in printing. 

Talc, as stated above, is often adulterated and hence its color 
is not a sure criterion of value. It should be tested for gypsum, 
calcium carbonate, mica, iron and sand. The usual test for 
calcium carbonate is by boiling with acid and noting the loss 
in weight, but if the acid used is too strong the test may be 
erroneous because the solvent action includes other portions of 
the filler. Good grades of talc should not contain over 1 to 2 
per cent of oxides of iron or over 3 to 4 per cent of CaC0 3 . 
Talc may be readily distinguished from clay by moistening with 
a little cobalt nitrate solution and warming over a flame; the 
talc gives a pinkish color and the clay a strong blue. 



CHAPTER XI 
COLORING 

The importance of coloring matter to the paper industry is not 
always evident to the casual observer but it is at once realized 
when it is understood that very few papers are made without 
coloring matter of some kind. This is of course self-evident in 
the case of heavily colored papers, or even pronounced shades, but 
it is equally true of white papers, for very few of these are made 
of the natural color of the fibre. It may even be said that color- 
ing, as applied to the production of shades of white, is of much 
more importance than in the making of colored specialities, for 
the production of the former runs into far greater tonnage. It 
is also true that the maintenance of uniformity in a tinted white 
requires more attention and care than in the case of deeper 
colored papers, for a slight error in the amount of color used will 
make an appreciable difference in the resulting shade, while with 
deeper colors an error of the same magnitude will have hardly 
noticeable results. Variations in the color of the fibres used are 
also much more serious in the case of tints than they are with 
deeper colors. 

In coloring paper it is usually required that the shade of a 
sample be matched. When such a sample is submitted previous 
runs of paper should be looked over to see if anything of the same 
or a similar color has been made before. It is often the case 
that the records of former orders will show just about what 
coloring matters should be used and an engine can then be 
colored up and the paper compared with the sample as soon as 
it gets over the machine. When the shade desired is an entirely 
new one the use of a small beater, of a pound or two capacity, 
will be found very convenient. By using a weighed amount of 

306 



COLORING 



307 



stock in such a beater, sizing and loading as usual, and noting 
carefully the quantities of colors used, the amounts necessary for 
the larger engines may be easily calculated. The stock pre- 
pared in the small beater should be made into sheets on a hand 
mould and dried on a steam heated drying cylinder. The sheets 
may then be compared, either before or after calendering, with 
the sample submitted. When such records or equipment are 
not available a small part of the sample should be reduced to a 
pulp with a little water, being careful not to use so much that 
coloring matter is lost by being washed out. The first engine is 
then colored up to match this wet sample. Whichever of these 
methods is used a sample of the paper should be taken from the 
winders, as soon as the color gets thoroughly over the machine, 
and compared with the sample submitted. If the shade is not 
right then the proper changes should be made at once, both 
in the stock in the chest and in the other engines which are 
being prepared. 

In estimating the amount of dye to use due attention must be 
paid to the beating of the stock and the calendering of the finished 
paper. The more hydrated the stock has become from prolonged 
beating the less dye will be required for a given shade. Calen- 
dering and supercalendering also darken the shade. 

When a colored order is to be made it is desirable to start in 
the morning so that plenty of daylight may be available for match- 
ing the shade. The nature of the light used for color compar- 
isons is important and a subdued north light is generally con- 
sidered best. This should be from a window not affected by 
reflections from neighboring buildings. Whatever light is 
selected as a standard, it should be used for all color work as the 
same results cannot be obtained if south light is used one day and 
north light the next. Difficulties from variations of light are 
entirely avoided if one of the color matching outfits, or so-called 
"daylight lamps," is used. These vary more or less in quality 
but several excellent ones are on the market. To give the best 
results a lamp of this type should be used in a dark room. 

In comparing colors the first impression should be decisive as 



308 COLORING 

the eye becomes less sensitive by prolonged staring. If doubt 
exists after the first glance rest the eyes by closing them, or by 
looking at some distant object, and then make a second com- 
parison. When papers are being examined they should be 
folded to such an extent that their thickness prevents any light 
from being transmitted through them since it is the light reflected 
from the surface which it is desired to compare. It is also well 
to change the samples from side to side — that in the right hand 
being transferred to the left, and vice versa — since the relative 
positions of the sheets has an influence on their apparent 
colors. 

In the coloring of paper the materials used may be divided into 
two general groups, the pigments, which are for the most part 
insoluble materials, and the dyes, which are generally employed 
in solution. Each of these classes has certain advantages and 
disadvantages which must be taken into consideration in select- 
ing the coloring matter to be used in any particular lot of paper. 

Pigments. Pigments are as a rule very fast to light and have 
the added advantage that they increase the weight of the paper 
by acting as fillers. They are not generally so brilliant as the 
dyes and have been in most cases replaced by the latter. They 
have properties, however, which make them valuable for certain 
papers and they should not be overlooked because they are more 
or less old fashioned. Both pigments and paste colors may with 
safety be added directly to the beater though heavy colors such 
as the canary and orange pastes may advantageously be thinned 
with a little water to prevent the settling of lumps and to insure 
their thorough mixing with the stock. While coloring with 
pigments is a purely mechanical operation it is at the same time 
necessary to pay due attention to the nature of the materials 
used and to those of the substances with which they come in 
contact; otherwise trouble will be caused by using simultaneously 
substances which are injurious to each other. 

Natural mineral colors are obtained from numerous natural 
deposits but before being of value they must be ground and 
separated in some way from any coarse or gritty particles. The 



PIGMENTS 



3°9 



fineness of their particles never equals that of the pigments pro- 
duced by chemical means but the finer they are ground the better 
results they will give. In addition to this mechanical treatment 
some of the earth colors are also treated chemically and in some 
cases various shades are obtained by heating the colors to certain 
temperatures. The shades of the natural mineral colors are 
usually of a subdued rather than a brilliant nature but so far as 
permanence is concerned they are not equaled by any other 
class of colors. Among colors of this class which are of interest 
to the paper maker are ochres, and red and brown earth colors. 
Whites, which would also come in this class, such as clay, gypsum, 
blanc fixe, etc., are discussed in the chapter on fillers. 

Ochres depend for their coloring power upon ferric oxide or 
hydrated ferric oxide, and various shades from yellow to brown 
are found upon the market. The best are finely divided powders, 
soft to the touch, and possessing plastic properties; dark-colored 
brands of this nature are generally richest in coloring matter. 
Ochres are sometimes mixed, or "topped," with chrome yellow 
to produce more brilliant shades; such products possess the 
defects of chrome yellow and if used without proper precautions 
are likely to cause trouble. 

The red earths owe their coloring power to the presence of 
amorphous ferric oxide. This is the chief ingredient in red hem- 
atite, which is the basis for numerous colors. Other reds are 
obtained by heating to redness, clays which contain hydrated 
ferric oxide. This class of colors includes a number of "red 
oxides," varying from yellowish to bluish red, and also Pompeian 
and Venetian reds which are usually of less strength than the 
"oxides." 

Among the brown earth colors are "velvet," "umber" and 
"chestnut" brown which depend upon burnt ferric hydrate for 
their coloring power. True umber consists mostly of manganese 
silicate which is greenish brown in its natural state but becomes 
a rich deep brown on burning. 

These natural mineral colors are largely used in the production 
of wall paper, for which purpose their subdued shades, their fast- 



310 COLORING 

ness to light and their resistance to atmospheric influences render 
them especially suitable. 

Artificial mineral colors are still used quite extensively in the 
coloring of paper, though, as already stated, many of them have 
been replaced by aniline dyes. Among those which are still 
relatively important are chrome yellow, Prussian blue and 
ultramarine. 

Chrome yellow may be obtained in the paste form from the 
manufacturers of pigments or it may be prepared directly in the 
engine by adding first nitrate or acetate of lead and when this is 
thoroughly mixed following with a solution of potassium or 
sodium bichromate. This determines the precipitation of lead 
chromate upon the fibre, in a very finely divided state. The 
color produced is influenced by alkalis, very small amounts of 
which are sufficient to darken the shade. Heat also influences 
the shade to a marked extent which necessitates very careful 
handling of the paper on the driers if irregular results are to be 
avoided. As the lead salts used are readily soluble in cold water 
no heating is necessary at this point and for the purest yellows 
the size and alum solutions should also be cold when used. The 
choice between the ready made paste color and that prepared in 
the beaters is largely a question of personal preference. The 
paste colors are comparatively simple to use and the matching of 
shades is much facilitated when they are employed; on the other 
hand the production of the color in the beater aids in the fixing 
of the color and in the obtaining of even shades. 

Chrome yellow is very fast to light but is destroyed by hydro- 
chloric acid. As the lead salts are dangerous poisons, their use 
is not to be recommended, and whenever possible the substitution 
of yellow dyes would appear to be good policy. 

Chrome yellow may be converted into chrome orange, or basic 
lead chromate, by treatment with caustic soda or hot milk of 
lime. This color can be used for unsized papers only as it reverts 
to chrome yellow in the presence of aluminum sulphate. 

Prussian blue is classed with the mineral colors because of its 
iron content. It may be produced directly in the beater by add- 



PIGMENTS 311 

ing ferrous sulphate followed by potassium ferrocyanide; the 
white precipitate which is first formed is rapidly oxidized by 
exposure to air with the formation of the blue color. This action 
may also be hastened by the addition of bleaching powder or 
acid to the beater. As the ferrocyanide is the more expensive of 
the two ingredients any excess is carefully avoided and it is 
customary to use three parts of ferrous sulphate to two of the 
ferrocyanide although two parts of the sulphate are usually 
sufficient for the full development of the color. Prussian blue 
which has been oxidized in the beater sometimes causes the paper 
to turn red after some time. This can be avoided by washing 
the stock nearly free from acid or better by employing a Prussian 
blue prepared outside the beater and washed before use. 

Paper colored with Prussian blue has the peculiarity that 
exposure to sunlight partially decolorizes it; the full blue shade 
is, however, again developed when the paper is kept in the dark 
in contact with the oxygen of the air. Prussian blue is affected 
by alkalis, particularly caustic soda, which destroys the color 
with the formation of ferric hydrate; treatment with acid 
restores the color. When using it in the beater it is well to see 
that it is added while the reaction is slightly acid due to the 
presence of alum. 

Soluble Prussian blue is produced when a ferric salt is added 
to an excess of a solution of ferrocyanide. The soluble product 
also results if Prussian blue is boiled in a ferrocyanide solution. 
It is soluble in water but is precipitated by salts. 

Ultramarines are formed when aluminum silicate is calcined 
with sodium sulphide. In actual practice the sulphide is formed 
from the action of sulphur and carbon upon sodium sulphate or 
carbonate. 

Ultramarines are manufactured in various shades of blue from 
a greenish to a reddish tone and there are even pure greens 
which, however, find little use in coloring paper. They are made 
by heating mixtures of pure clay, sodium sulphate, sodium car- 
bonate, sulphur, silica and charcoal; the mixture after heating is 
finely ground and washed. The proportions of the ingredients 



312 COLORING 

vary with the different manufacturers but in general three grades 
are made as follows : 

i . Sulphate ultramarines are those made with sodium sulphate. 
They are the palest, are greenish in tint and are most easily 
attacked by alum. 

2. Soda ultramarines low in sulphur are pure blue and darker 
than the sulphate ultramarines. 

3. Soda ultramarines high in sulphur and silica are the darkest 
and have a reddish tinge. They are the most resistant to 
alum. 

The finished ultramarine contains sodium, aluminum, silicon, 
sulphur and oxygen; its actual constitution is not known and no 
theory so far proposed accounts for all its properties. Ultra- 
marines are absolutely fast to light and are not changed by expo- 
sure to the atmosphere or by weak alkalis. They are decom- 
posed by mineral acids with evolution of hydrogen sulphide and 
destruction of the color. They are darkened by moisture which 
is taken advantage of by unscrupulous dealers who add water, 
glycerine or molasses to make them appear of greater strength. 
For this reason ultramarine should not be purchased on the basis 
of its appearance but actual coloring tests should be made. The 
different products vary in the fineness of their particles and the 
ease with which they mix with water. Both of these points 
should be considered since if they are not satisfactory spots or 
color streaks are likely to appear in the paper. 

When used for tinting in the production of white papers ultra- 
marines give bright effects which are hard to equal with other 
coloring materials. If they are used for deeper colors the two 
sides of the sheet are apt to vary in shade because of the loss of 
pigment in passing over the suction boxes. 

Another pigment which is still used occasionally for gray or 
black papers is lamp black. If used in large proportions it tends 
to cause streaks and specks in the paper and to make it smut 
badly. Its low specific gravity makes it difficult to handle with- 
out getting it all over the beater room and uniform results are 
hard to obtain because the shade depends so much on the length 



ARTIFICIAL ORGANIC COLORS 313 

and nature of the beating which the stock has had. Lamp black 
is being replaced by various mixtures of soluble dyes. 

Natural Organic Colors. Colors of this class, of a vegetable 
or animal origin, were formerly much used in coloring paper but 
they are no longer employed to any extent because of the better 
and cheaper results obtained with the coal tar colors. For this 
reason brief mention of their names and properties is all that 
seems desirable. 

Annatto is derived from the fruit of the annatto tree and 

gives shades of orange. It is costly and fugitive. 
Turmeric is prepared from the roots of Curcuma tinctoria. 

It dyes paper pulp a direct yellow which is fast to acids 

but is sensitive to light and alkalis. 
Weld is obtained from the blossoms of Reseda luteola. It 

gives various shades of yellow according to the mordant 

used. 
Quercitron is the powdered bark of Quercus tinctoria. It 

gives yellow shades when used in the same manner as weld. 
Safflower is obtained from the petals of Carthamus tinctoria. 

It gives pinks of great beauty but they are fugitive to light 

and air. 
Redwoods. Various species of Caesalpinia have been used 

for the dyeing of pink and reddish shades which are not 

very fast to light. 
Cochineal is obtained from the cochineal insect and was 

formerly used as a pink for toning white papers. 
Cutch or Catechu is the dyestuff obtained from Mimosa 

catechu. It gives shades of brown which are fast to light, 

acids and alkalis. 
Logwood is obtained by extracting Haematoxylon campe- 

chianum. It is used for blacks in conjunction with iron 

salts and tannic mordants. 

Artificial Organic Colors. This class includes all the so-called 
coal tar colors or aniline dyes. They are superior to other color- 
ing matters in brilliancy and purity of shade, coloring power, 



314 COLORING 

solubility and ease of application and their chief drawback is lack 
of fastness to light. 

In using these dyes the method of working depends on the 
fibre to be dyed and the nature of the coloring matter used. A 
knowledge of the methods employed in textile dyeing is of con- 
siderable assistance though the impossibility of thorough washing 
in the beater renders impractical the use of many of these 
methods. Moreover since vegetable fibres only are used in 
paper making any methods which are applied to wool or silk are 
only of abstract interest to the dyer of paper. It must be borne 
in mind that the different fibres in mixed stock may have different 
affinities for the coloring matter and by taking it up in different 
degree cause an uneven or variegated appearance. If clear light 
shades are desired only bleached pulp may be used while the 
heavy,. deep colors can with advantage be obtained on unbleached 
stock. 

Fillers which take up the dyes assist in obtaining even shades 
and whenever possible the filler should be selected with this object 
in view. To allow the filler to absorb the greatest amount of 
color it should be added after the dye but before the size. 

The combination of the filler and the dyestuff is regarded by 
some as a chemical phenomenon while others consider it purely a 
physical action depending on the ability of the filler to form 
colloidal solutions. The amount of dye taken up by different 
fillers has been determined by Heuser 1 who gives in the following 
table the percentage of the added dyestuff taken up by the filler 
when 10 grams of the latter are treated with 0.4 gram of color. 

1 E. Heuser: Wochbl. Papierfabr., 1914, 2288 and 2470. 



ARTIFICIAL ORGANIC COLORS 



315 



Color 



Malachite green. . . 

Crystal violet 

Manchester brown. 

Safranine 

Chrysoidine 



96 
99 
97 
84 
96 

66 
60 
58 
68 

25 

Diamine green 58 

Dianil blue 96 

Diamine violet 

Diamine heliotrope 60 

Diamine purpurine 59 



Alkali blue .... 
Acid magenta. . 

Ponceau 

Cotton scarlet. 
Napthol yellow. 



Asbes- 
tine 



Blanc 
fixe 



Bohemian 
earth 



China 
clay 



Kaolin 



72.75 
64. 
72 
41 

55 



Talc 



49-95 
60.56 
40.62 
30.06 
35-52 

35-26 
49-89 
54-27 
60.12 

25-45 

50.00 
60.76 
69.11 

65-85 
60.48 



The following figures by H. Strom x show the color absorbed in 
grams by 1 gram of filler from 100 c.c. of 0.1 per cent solution of 
the dyestuff . 



Malachite green 

Safranine, cone 

Paper Scarlet ex 

Dianil yellow R 

Dianil red R 

Eosine ex. 5 B 

Paper deep black, cone. 



Asbestine 



0.005786 
O.007752 
0.003715 
0.005786 
0.008039 
o . 000900 
0.005970 



Blanc fixe 



.003715 
.004877 
.002251 
.006712 
.OIOOOO 
.002764 
.007277 



Talcum 



O.005058 
0.007752 
0.003237 
0.004518 
O .006526 
O.002764 
0.004877 



Kaoli 



O.008425 
O.009941 
0.001914 
o .005603 
o .006526 
0.002936 

O.C03633 



China clay 



0.008425 
0.009941 
0.003237 
O.004518 
o . 009404 
0.002593 
0.006712 



Not all dyes of the same class are taken up to the same extent 
by the same filler. Acid dyes can be removed almost com- 
pletely from fillers by washing with hot or cold water; basic colors 
fix themselves on silicates but even basic colors can be washed 
out of blanc fixe. 

Apart from all questions of the theory of dyeing the coloring 



Strom: Wochbl. Papierfabr., 44, 4516. 



316 COLORING 

of paper pulp is not only a question of forming and fixing colored 
precipitates where pigments are concerned but also of fixing the 
soluble colors firmly on the fibres by means of mordants. Coal 
tar colors which form no precipitates with metallic salts and 
which are not fixed on the fibres when the pulp is acidified are of 
no use in coloring paper. The mordants in some cases serve to 
fix the color upon the fibre and make it more fast to washing, 
light, etc., while in other cases they combine with the dye as an 
essential constituent without which it would be uncolored or a 
worthless shade. Mordants are of two general classes, acid 
mordants, such as tannic acid and the fatty acid compounds used 
for fixing basic dyes; and basic mordants, consisting of the 
hydrated oxides of the heavy metals as tin, copper, chromium, 
iron, aluminum, etc., which serve for fixing the acid dyes. Basic 
mordants are employed in the form of soluble salts, such as the 
sulphate or acetate of aluminum, which react with the fibre with 
the deposition of the base which then attracts and fixes the color. 
Time is required for this reaction and different mordants give 
different colors with the same dye. Cotton has little affinity for 
ordinary metallic salts but if they are present in very basic con- 
dition it may decompose them with the loose fixation of metallic 
hydroxides. Tannin on the other hand has a direct affinity for 
cotton and may be still more firmly fixed by the use of tartar 
emetic or glue. Linen is similar to cotton but is even more 
difficult to dye. While not strictly a mordant rosin size gives to 
fibres some of the properties of animal fibres and enables them 
to take up many colors without the use of any other mordant. 

The use of mordants, other than rosin sizing, is not nearly so 
general in the paper industry as in textile work and in many 
mills they are never employed. 

The water used in dyeing operations may have a considerable 
influence on the results. Finely divided vegetable impurities 
have little effect on either colors or mordants but inorganic im- 
purities are much more serious. Hard water due to carbonates or 
bicarbonates of calcium or magnesium may cause partial pre- 
cipitation of basic colors; if it is necessary to use such water for 



DIRECT COTTON COLORS 



317 



dissolving basic colors it should be corrected by adding a very 
slight excess of acid, preferably acetic acid. Salts of iron in the 
water are particularly bad as they discolor the fibres and act 
as mordants with the production of bad shades. 

Dyes should not be added to the beater in the dry state except 
in very special cases, as sooner or later trouble with color specks 
will be encountered. They should be dissolved in soft, or con- 
densed, water and strained through a hair sieve or through wet 
flannel before being used. The amount of water necessary varies 
greatly but in general is more for basic than for acid dyes; with 
some of the former it may be necessary to use as much as 200 
lbs. of water for 1 lb. of color. Most colors may be heated nearly 
to boiling without danger, but a few, as auramine, methyl green, 
etc., are injured by boiling and should not be heated above 
160 to 170 F. If the color separates from solutions which have 
been made some time it may be redissolved by heating and 
stirring. Some colors are insoluble or slightly soluble in water 
and in this case equal parts of methyl alcohol and water may be 
used. 

The dyestuffs are variously classified by different writers. 
Direct or substantive colors are those which color the fibres 
directly without the use of a mordant; they are fully developed 
colors and always give the same shade, either weaker or stronger 
according to the amount used. Mordant or adjective colors are 
those which must be treated by chemical means in order to 
develop the true colors. This group forms with metallic oxides 
insoluble precipitates or lakes on the fibre. Colors which are of 
interest to the paper maker may be divided into four principal 
groups as follows: (1) direct colors, (2) basic colors, (3) eosines 
and rhodamines and (4) acid colors. The grouping of the acid 
colors separately is for practical rather than scientific reasons 
since the dividing line between the acid and the direct cotton 
colors is not at all sharp. 

Direct Cotton Colors. These may be used on unmordanted 
fibres in a neutral or alkaline condition and they can be used 
mixed with each other in the same bath. Acid colors may usually 



318 COLORING 

be mixed with the direct colors and used together though basic 
colors should never be mixed with direct colors either dry or dis- 
solved. Dyeing with the direct colors is best done at the boiling 
temperature though it may also be done warm or even cold. If 
the stock is not heated the backwater is apt to be colored. Salt to 
the extent of 75 lbs. to a 1,000-lb. beater is also desirable to assist 
the fibre in taking up the dye. Under most conditions the 
colors tend to bleed from the fibres when they are mixed with 
white fibres so that they are not satisfactory for granite papers. 
This can be prevented to a certain extent by topping with basic 
colors and it is also claimed that by adding 10 lbs. of Glauber 
salt per 100 lbs. of fibre and boiling for three quarters of an hour 
fastness to water can be insured. The direct cotton colors are 
usually precipitated by lime and magnesia and water containing 
these substances should be corrected by boiling with soda 
ash. 

These colors are particularly desirable for blotting papers and 
tissues where sizing cannot be used; they are also equally ser- 
viceable for sized papers. They, exhaust well and a colorless 
backwater is usually obtained. They vary greatly in fastness to 
light, some being fully as fugitive as the basic colors while others 
are among the fastest colors known. Certain of the direct blues 
are increased in light resistance by adding a little copper sulphate 
to the beater after the dye has been taken up by the fibre. When 
1 per cent or less of the dyestuff has been used 2 per cent of cop- 
per sulphate should be added but if over 1 per cent of dye has been 
employed an equal weight of the sulphate will be sufficient. 

Basic Colors are salts of organic bases of artificial origin, the 
base containing the color bearing group. Most commercial 
basic colors are hydrochlorides, though sulphates, acetates, oxa- 
lates, nitrates or even double salts of hydrochloric acid and zinc 
chloride are also met with. In rare cases the color base is used. 
All basic colors are decolorized by reducing agents as zinc and 
hydrochloric acid. Some are decomposed into other substances 
so that the color cannot be regenerated but with most a colorless 
or "leuco compound" is formed which is easily oxidized to the 



EOSINES AND RHOD AMINES 319 

original color. In dyeing with basic colors the salts decompose, 
the basic part combining with the acid present in the fibre or 
fixed thereon by mordanting with tannic acid. The nature of the 
mordant or of the fixing metal does not greatly affect the shade 
of any given dye. 

Basic colors have very great tinctorial power and are generally 
of pure and brilliant shades. They are fugitive to light but 
because of their great coloring power they are extensively used 
where permanence is not of the utmost importance. The 
affinity of all fibres for basic dyes is not the same, so when mixtures 
are being treated uneven dyeing may result; this can be avoided 
to a great extent by adding a little alum before the color or by 
adding the dye in a very dilute condition. When the fibres have 
a considerable affinity for the color, as with sulphite and jute, 
the dyeing may be done with the aid of rosin and alum or even 
alum only but for absolute fastness, as for use in making granite 
papers, mordanting with tannin is necessary. With unbleached 
sulphite there is a very strong tendency to absorb the color and 
to avoid uneven dyeing it is well to use the color in very dilute 
solution. For ground wood pulp basic colors are especially 
suitable and the dyeing should be done hot. 

Basic colors may be used mixed with each other but never 
mixed with either acid or direct colors since precipitation re- 
sults. If it is necessary to use both classes of color they should 
be dissolved separately and added separately to the beater. 
Many of the lakes formed by basic and direct colors are decom- 
posed at 70 C, or even below, so where both are used it is well 
to avoid high temperatures. The use of acid and basic colors 
together gives colorless backwater; to obtain the best results 
it is well to use the basic dye first and top with the acid 
color. The exhaustion of the color is also aided by the filler 
which readily takes it up at comparatively moderate tempera- 
tures. 

Eosines and Rhodamines. Commercial eosines are alkali 
salts of chlorine, bromine, iodine or nitro-substitution products 
of fluorescein or some of its derivatives, while rhodamines are 



320 COLORING 

basic hydrochlorides of organic bases. Rhodamine B, for in- 
stance, possesses both acid and basic properties while the eosines 
have the properties of feeble acids. All of this group form 
leuco compounds on reduction and regenerate more or less rap- 
idly on oxidation but not always to the same compound as the 
halogen is frequently removed by the reducing agent. 

The eosines are mostly soluble in soft water or dilute alcohol, 
but with hard water insoluble lakes are formed so that such 
water must be corrected with soda ash. Rhodamines may be 
dissolved as with basic colors. Solutions of the eosines show 
more or less fluorescence particularly in alcoholic solution or 
in the presence of ammonia. Eosines are fast to alkalis but 
not to mineral acids; they are also affected by alum to a harm- 
ful extent so that an excess of the latter should be avoided. 
They have very slight affinity for vegetable fibres and their 
fixation is due largely to the sizing. They form lakes with 
metallic salts, those with lead being particularly brilliant; to 
obtain the best shades, therefore, sugar of lead may be used in 
the beater. 

Eosines dye shades from yellowish to bluish red; they are 
remarkably brilliant but are very fugitive. Rhodamines are 
also very brilliant and are much faster. They are not much 
used on cotton because they cannot be permanently fixed on 
the fibre without impairing their brilliancy. 

Acid Colors. Acid colors are of three groups (i) nitro com- 
pounds, (2) azo compounds and (3) sulphonated basic colors. 
They are decolorized by reducing agents but are differently 
affected; nitro compounds are converted into amino compounds 
from which the coloring matter cannot be regenerated; azo 
compounds decompose with breaking up of the azo group and 
cannot readily be linked up again; while the sulphonated basic 
colors form leuco compounds from which the color can be 
regenerated. 

Acid colors can De mixed with each other to produce com- 
pound shades. They are not suitable for unsized papers as they 
have comparatively little affinity for fibres and cannot be fixed 



VARIOUS APPLICATIONS 321 

on cotton or linen to resist washing. Rosin sizing is essential 
for good results especially for deep shades and better fixation is 
obtained if the color is added long enough before the size to 
insure thorough mixing before the latter is added. As a rule 
acid colors have comparatively little tinctorial power. They 
are quite variable in fastness to light but are generally more 
fast than basic dyes. 

Miscellaneous. Not mentioned in any of the previous groups 
are certain organic pigments especially the indanthrenes. These 
belong to a class of vat dyes which in textile work yield shades 
which are remarkably fast to light. While a number of vat 
colors are used in textile work the only ones which have been 
tried for coloring paper are the blue indanthrenes. These are 
sold in the form of paste colors, being insoluble in water and 
dilute acids or alkalis. They are used in the same way the 
pigments are and have the common fault of all paste colors 
that the strength of the color is continually changing because 
of the loss of water through evaporation. The colors obtained 
with indanthrene, at least where tints are concerned, are not 
particularly bright and as a class they have little to recom- 
mend them except their great fastness to light. 

Various Applications. The foregoing remarks apply chiefly 
to the coloring of paper stock in the beater. The coloring of 
coating to be applied to the surface of the paper follows similar 
lines, except that the colors used must in general be fast to 
alkalis since satin white contains considerable amounts of free 
lime and the casein is usually treated with an excess of alkali in 
dissolving. When pigments are used in coating they must be 
very finely divided and easily broken down into their ultimate 
particles since lumps of color will crush when calendering and 
form spots or streaks. 

A third method of coloring is that known as stuffing, padding, 
or calender staining. Here the color is applied to the surface 
of a web of paper as it passes through the calenders. Soluble 
colors are necessary for this work and for absorbent, or very 
slightly sized, paper the solution may be made with water. If 



322 COLORING 

the paper is hard sized, the color may be dissolved in denatured 
alcohol to make it penetrate the paper slightly. Acid dyes are 
much used for this type of work. 

For the production of heavy colors a saving of dye is some- 
times made by coloring the stock partly in the beater and when 
the paper is partly dried on the first section of driers running 
it through a vat of the color solution, then through squeeze 
rolls and finally over the rest of the driers. 

Testing Colors. The tests which it is desirable to apply to 
colors are those which will show whether the material is of the 
same shade and strength as the standard. In the case of new 
samples it is necessary to compare their color and tinctorial 
power with dyes already in use, and also to apply tests to show 
whether they are sufficiently fast to the chemicals with which 
they will come in contact. 

The most satisfactory method of testing colors, though by 
no means the quickest, is to color up a weighed amount of stock 
which has been beaten, sized and loaded in a small beater. 
Sheets made from this stock and dried will then give a perma- 
nent record of the shade and strength of the color in question. 
This method can be applied equally well to dyes and pigments 
but it is not very satisfactory for tints, such as the blue- or 
pink-whites, of the book or writing paper class. 

With soluble colors the following method has proved satis- 
factory in most cases. Prepare a solution of one part of the 
dye in iooo parts of water, noting carefully any insoluble resi- 
due. From this solution remove two samples of 50 c.c. and 
25 c.c. respectively, place them in separate beakers of about 
300 c.c. capacity, and dilute each to exactly 250 c.c. From a 
stock supply of dry, bleached, sulphite fibre prepare strips of 
the same size which will fit easily into the beakers of the diluted 
dyes. Plunge these strips into the solutions for exactly one 
minute, remove, drain and air dry. They can then be com- 
pared with the standard strips for shade and strength. For 
some of the very strong basic colors it is well to use 25 and 
10 c.c. instead of 50 and 25. It is obvious that this test is 



TESTING COLORS 323 

comparative only and that the quantities and volumes may be 
varied to suit the wishes of the observer. 

With pigments the following test has proved very convenient. 
Weigh into a porcelain cup 100 grams of clay and 3 grams of 
the pigment. Mix this with 70 to 75 c.c. of water and then 
add 60 grams of a casein solution containing exactly 12 grams 
of casein. Mix the contents of the cup very thoroughly and 
by means of a brush or some sort of a scraping device apply a 
very thick coat of the mixture to small sheets of white paper. 
When these sheets are dry, preferably air dried, they are com- 
pared with the standard sheets for color. This test also is 
comparative only and to make it of value the same clay, casein 
and paper must be used in every case. 

Fastness to chemicals may be determined by treating a dilute 
solution of the dye with small quantities of the chemicals with 
which it will come in contact. By making the tests with solu- 
tions of definite strength and using the same volumes each time 
the effects of the chemicals on the different dyes can be more 
readily compared. It is well to make the test first by noting 
the effect of standing several hours in the cold and finally by 
bringing the solutions just to a boil. 

For use in vulcanized fibre the colors should be fast to zinc 
chloride solution. This is best determined by coloring some of 
the stock with the dye to be tested, passing the sheet through 
a bath of zinc chloride of the correct strength, and finally 
washing. This will show whether the color is affected and 
also whether it will bleed during the washing of the finished 
product. 

Fastness to light may be determined by exposing strips of 
paper, colored with the dye to be tested, in a printing frame 
in such a way that part of the strip is protected from the light. 
If daylight is used it is difficult to duplicate the test because 
of the variation in the quality of the light from day to day and 
at different times of the year. This can be avoided by using 
artificial light rich in the ultra violet rays which are the ones 
most active in the fading of colors. Such apparatus intensifies 



324 COLORING 

the fading effect and enables results to be obtained in a com- 
paratively short time. 

It is very seldom that it is necessary to determine what dye 
was used in coloring a given sample of paper, usually it is suffi- 
cient to be able to match the shade. The determination of 
the dyestuff used is a difficult matter at best and is greatly com- 
plicated when more than one dye was used, which is generally 
the case with colored papers. If it is necessary, the scheme 
proposed by A. G. Green 1 for the determination of dyes on 
vegetable fibres is probably the best one to follow. The iden- 
tification of the dyes themselves may be carried out according 
to the schemes of A. G. Green 2 and S. P. Mulliken. 3 The 
general properties of the different classes of dyes have already 
been described and it is usually sufficient to determine to what 
class or group the sample belongs, since this information fixes 
the dye method to be used. 

It is often desirable to know whether a commercial product 
is a simple dye or a mixture. If the dyes have been mixed in 
the powdered state, the fact that it is a mixture may be ascer- 
tained by taking a small sample on the end of a spatula and 
blowing it onto a piece of wet, white blotting paper. Each 
speck of color gradually dissolves and the various colors of a 
mixture show very plainly and can be tested by chemical means. 
When the coloring matters' have been mixed in solution and 
evaporated together this test fails. For such cases the dye can 
be tested by making a succession of dyeings of wool or cotton 
skeins in the same dye bath. If the dye is a mixture the first 
and last skeins will differ in shade. 

1 Green: J. Soc. Dyers and Colorists, 1907, 252. 

2 Green: J. Soc. Chem. Ind., 1893, p. 3. 

3 Mulliken: Identification of Pure Organic Compounds, Vol. Ill, Commercial 
Dyestuffs. 



CHAPTER XII 
COATED PAPERS 

The class of papers variously known as coated or glazed, and 
in England as art papers, has been developed within compara- 
tively recent years in response to the demands of the printers 
for a paper on which half-tones could be reproduced to good 
advantage. The essential feature of such papers is a thin layer 
of mineral matter and adhesive applied to the surface of an 
ordinary sheet of paper, the function of the mineral matter 
being to form the surface for printing, while the adhesive is 
merely added to hold this mineral matter on the paper and 
prevent its being removed by the ink. The coating covers the 
individual fibres on the surface of the paper and in addition rills 
in any hollows or irregularities between them so that when the 
paper is calendered there results a fine, smooth, even, and con- 
tinuous surface which permits the finest dots of the half-tone 
screens to take perfectly. Such papers are used for lithographic 
work, for magazine and other printing and especially for the 
high class half-tones in catalogues and advertising matter. 

While coated papers possess advantages from the standpoint 
of the printer, they also have certain defects which are of a 
quite serious nature. The body stock is frequently made of 
inferior materials while the coating, due to its nitrogenous 
nature, is peculiarly subject to decay and to the attacks of 
insects, especially when stored in warm, damp places. The 
paper is also very heavy and bulky so that books made from it 
are difficult to handle and, moreover, it has very poor folding 
or bending qualities and is therefore much more liable to injury 
than uncoated papers. It is by no means certain that coated 
papers will not deteriorate within a comparatively short time 

325 



326 COATED PAPERS 

to such an extent that matter printed on them will be valueless 
and for this reason they should never be used for documents of 
permanent or historic value. 

The paper, or body stock, to which the coating is applied, 
need not be of the highest class since it is entirely covered by 
the coating, and hence inferior materials are frequently used in 
its manufacture. In fact in Europe ground wood is often one 
of the principal ingredients though it is a finer quality of ground 
wood than is generally made in this country. A practical limit 
is set to the use of low-grade stock by the fact that the coating 
is more or less translucent and does not prevent dirty or shivey 
stock from showing in the finished paper. 

Some of the qualities demanded in paper for coating are 
regular formation, softness and pliability, freedom from fuzz 
and cockles, uniformity of finish, and medium sizing. The 
regular formation is essential if uniform finish is desired in the 
coated paper, and softness and pliability are necessary if the 
paper is to run well on the c oaters since a hard, rattly sheet will 
not lie flat, tends to curl on the edges and does not take the 
coating well. Each little fibre which stands up from the sur- 
face in a fuzzy sheet seems to attract the coating so that it 
causes a mottled effect; this is particularly noticeable when 
the coating is tinted since the color seems to concentrate itself 
round the base of each fibre. One of the most important qual- 
ities to be considered is the sizing of the sheet since if it is too 
hard sized the coating tends to lie on the surface and be streaky, 
while if it is too slack sized the adhesive will be absorbed, per- 
mitting the coating to be weak, or necessitating the use of an 
abnormally large amount of adhesive. Defective sizing is much 
more serious when glue is used than when casein is employed 
since the temperature of the drying lines is generally high enough 
to keep the former liquefied and thus permit its absorption. 

The coating mixture is nearly always applied to the paper by 
machinery, several different types of apparatus being used. In 
one the mixture is transferred from a roller revolving in a trough 
to a felt or brush, and from this to the surface of the paper; 



APPLYING THE COATING 



327 



in another the paper passes under a roller which is immersed 
in a tank of the coating mixture and the excess is removed by- 
squeeze rolls. In either case 
the coating is immediately 
smoothed out and brought 
into good contact with the 
paper by means of brushes 
working across its surface 
with a reciprocating motion. 
The first of these brushes is 
comparatively coarse, but they 
gradually become finer till the 
last, which is very fine, to 
eliminate the marks made by 
the first. The arrangement 
of this coating machine is in- 
dicated in Fig. 39. After 
leaving the brushes the paper 
passes through a drying gal- 
lery heated by steam coils or 
a current of hot air and when 
thoroughly dry is reeled up 
ready for calendering. The 
amount of coating applied by 
this process varies with the 
purpose for which the paper 
is made and may be anything 
from a wash coat up to 35 per 
cent of the weight of the fin- 
ished paper. According to the 
type of coating machine used, 
both sides may be coated at 
one operation with the same 
color or each side may be 
coated separately with the 
same or different colors. 




328 



COATED PAPERS 



The adhesives used in coated paper are chiefly glue and 
casein, though starch and albumen have been used to some 
extent and many others have been proposed from time to time. 
The amount used varies with the different mineral matters, 
satin white requiring much more than blanc fixe, while clay 
occupies an intermediate position. If too much adhesive is 
used the paper tends to curl, the color is not so good and the 
coating is less porous so that when printed the ink is apt to 
offset and to crawl or mottle instead of lying flat. Such paper 
also takes a lower finish on calendering than when less adhesive 
is employed. From the point of view of the printer, as well as 
for reasons of economy, it is therefore desirable to use as little 
adhesive as possible. On the other hand if too little is used, 
the coating will "lift" or "pick" when printed, especially if 
heavy or tacky ink is used. This imposes a minimum beyond 
which the adhesive cannot be reduced, while as a matter of fact 
this minimum is seldom even approached because the many 
variable conditions render it necessary to employ a large factor 
of safety. In good work it is seldom possible to use less than 
15 lbs. of dry casein to 100 lbs. of dry clay and much more 
frequently 18 to 20 lbs. are used, while with glue the quantity 
employed is about 20 to 25 lbs. 

The influence of the amount of casein in the coating on the 
time required for linseed oil to saturate the paper, which may 
be taken as a measure of the rapidity with which ink will pene- 
trate, is well shown by the following experimental data. 



Grams of casein 
per 100 grams clay 


Time in seconds for 
oil to saturate 


Grams of casein 
per 100 grams clay 


Time in seconds for oil 
to saturate 


IO 

IS 

20 


20 

37 

125 


25 
3° 


780-1020 

Does not penetrate 




1 





The mineral matter employed in coating paper may be clay, 
blanc fixe, satin white, talc, or a number of other substances 
and they may be used singly or in mixtures of two or more. 



FINISHING COATED PAPERS 329 

The character of the finished paper depends very largely upon 
the mineral matter used and many different effects can be 
produced by a careful blending of the various substances. Satin 
white gives the smoothest coating and the highest finish of any 
of these materials, clay gives a lower finish, while blanc fixe 
takes less polish than either, thus by a proper selection nearly 
any desired finish may be obtained. The qualities demanded 
in a coating substance are good color, freedom from grit and 
the property of working up to a good, fluid mixture when the 
adhesive is added. For tinted or colored papers it should also 
be free from all traces of acid since this might injure the shade. 
The color demanded of a coating material is in general much 
brighter than that which a filler is expected to possess and the 
price paid is correspondingly higher. 

In addition to the two main ingredients in the coating mix- 
ture, other substances are frequently used in smaller amounts 
for special purposes. Soaps or waxes, either in solution or in 
the form of emulsions, are added with the object of improving the 
finish; antifroth oils are used to prevent excessive foaming of 
the coating mixture; glycerine, or some of its substitutes, is 
added to give the coating increased pliability or folding power 
and salt is sometimes employed to reduce the curling tendency 
of the paper. Nearly every manufacturer has in use some such 
modification of the regular process which he generally considers 
a secret, though it often proves to be quite widely known. There 
is thus opened a very wide field for the employment of chem- 
istry in the coating industry and it is probably safe to say that 
it offers more and harder problems than any other department 
of paper making. 

The finish imparted to coated paper depends on the way in 
which it is calendered as well as upon the materials of the coat- 
ing; the damper the paper the higher the finish. There is a 
limit, however, to the amount of moisture which can be advan- 
tageously left in coated paper which is to be calendered, since if 
it is too high the paper tends to crush or blacken and the color 
is seriously injured. The amount of moisture which will cause 



330 COATED PAPERS 

this varies with different papers and with the pressure put on 
the calenders so that no invariable limit can be set. It is, 
however, safe to say that if the paper contains much over 5 to 6 
per cent of moisture, exceeding care will have to be used in 
calendering it. The finish of paper may be considered as com- 
posed of two factors, smoothness and shine. The former is 
essential to good printing while the latter is not, and since it is 
highly inartistic as well as seriously injurious to eyesight, it 
would seem well to avoid it as far as possible. This is being 
done by producing dull finish or mat papers in which the smooth- 
ness is imparted by a light calendering, which is done in such a 
way that little friction is employed, so that the polishing effect 
is slight. Another method is to give a very thin wash coat, on 
the coating machine, over a paper which has been thoroughly 
smoothed. This produces a peculiarly velvety surface which 
takes half-tone effects with very beautiful results but possesses 
the slight defect that it is easily scratched, a slight stroke with 
the finger nail sufficing to cause a distinct mark. Careful selec- 
tion of materials which do not readily take a high finish, such 
as blanc fixe, barytes, precipitated chalk, etc., materially assists 
in the minimizing of this defect and also aids in the production 
of dull finish papers of the first class. Although papers with a 
very high glossy finish are still largely demanded, yet these dull 
finish papers are rapidly growing in favor and it is anticipated 
that they will become more popular as they become more 
widely known. 

The printing qualities of coated papers are largely influenced 
by the kind of adhesive used as well as by the amount. Glue 
coating possesses the property of taking ink especially well while 
casein is slightly more difficult to handle. This difference 
caused trouble when casein was first introduced and its general 
use was delayed because of the prejudice of the printers. It is 
often claimed that the reason for this difference lay in the acid 
reaction of glue coated papers and the alkalinity of those coated 
with casein. This explanation is probably erroneous since it 
has been found that casein coated papers, except those contain- 



GLUE 



33 1 



ing satin white, are normally acid to litmus in spite of the fact 
that an excess of alkali is almost always used in preparing the 
casein solution. Except with inks which are exceedingly sensi- 
tive to acids or alkalis the reaction of the papers is probably 
of very little importance since printers practically never make 
any difference, in regard to the ink used, between ordinary 
coated papers and those containing considerable satin white 
which are strongly alkaline. 

Glue. Of the adhesives used for coating paper glue was the 
first, and for a long time practically the only one, and although 
it has been largely superseded by casein it is still used to some 
extent. It was formerly the custom, in many cases, for the 
consumer to manufacture his own glue but it is better practice 
to purchase it of some reliable dealer as the supply obtained 
in this way is likely to be more uniform. For convenience in 
handling, the ground glue is to be preferred to the sheet glue, 
since it requires very little time for soaking and the solution 
can be quickly prepared. The quality best suited for coated 
paper work is a good grade of hide glue but it is undoubtedly 
true that much inferior material is used, either intentionally 
because of the apparent saving in cost, or unintentionally be- 
cause of its substitution by unscrupulous dealers. Poorly made 
glue is apt to give trouble by frothing and it probably lowers 
the quality of the paper in which it is used though from the 
numerous variables entering into the manufacture it is frequently 
impossible to locate the cause of inferiority with certainty. 

Glue for coating paper should be of good color, free from 
objectionable odor, of good strength, nearly neutral in reaction 
and for some purposes free from grease. The grease if present 
in appreciable amount tends to make " birds'-eyes " in the coat- 
ing and thus cause defective printing. Too much grease also 
lowers the clay carrying power or strength of the glue. If on 
the other hand, the glue is entirely free from grease, the coating 
dusts on the calenders and the paper will not take a good finish. 
This reason for dusting was suspected by one manufacturer 
who made his own grease-free glue and when a small amount 



332 COATED PAPERS 

of fat was added to the glue solution the trouble entirely 
disappeared. 

A rapid semi-quantitative test for grease may be made by 
coloring the glue solution intensely with some aniline dye and 
then brushing it lightly onto white paper. If grease is present, 
spots or " birds'-eyes " will form and the number of these is 
roughly proportional to the amount of grease. This test also 
gives an indication of the way the coating mixture will spread 
under the action of the brushes. The best quantitative method 
for the determination of fat is that of Kissling which is carried 
out by dissolving 20 grams of the sample in 150 c.c. of water 
containing 10 c.c. of hydrochloric acid (sp. gr. 1.20). This is 
heated three to four hours on the steam bath, using a reflux 
condenser, and after cooling the fat is extracted by means of 
petroleum ether, which is then evaporated off and the residue 
dried and weighed. Good grades of glue may contain 0.1 to 
0.6 per cent of fat, but it is safer to use those which run nearer 
the lower figure. 

The presence or absence of acidity in glue is of even more 
importance than the question of fat since in many instances 
the colors used are affected by the acid to such an extent as to 
cause serious variations in shade. The acidity of glue may be 
determined with fair accuracy by dissolving 1 gram of the sample 
in 500 c.c. of water, adding a few drops of phenolphthalein solu- 

N 
tion and titrating with — alkali. This gives all free acid, 

10 

organic as well as mineral, and since a number of acids may be 

present it is well to express the total quantity as the equivalent 

percentage of sulphuric acid. The percentage of acid in glues 

is quite variable, often running as high as 1.2 per cent, but for 

use with delicate colors it should not be over 0.2 to 0.3 per cent. 

The strength of glue is often considered to be proportional to 

the firmness of the jelly which it forms, but experience has 

shown that the amount of clay which a sample will hold is not 

always in accord with its jellying powers. A much more reliable 

test for strength is described under casein. 



CASEIN 333 

Coated papers in which glue is used are generally slightly 
acid in reaction and they possess certain qualities of surface 
and porosity not present in casein-coated papers. The change 
from glue to casein was delayed for this reason since it involved 
also a change in inks and the technic of printing, but the lower 
price of casein enabled it to force its way gradually in till now 
it has almost wholly replaced glue in all ordinary grades of 
coated papers. 

Casein. Casein is a nitrogenous body which is present in 
milk to the extent of about 3 per cent by weight. It may be 
separated from milk either by the action of acids or rennet, but 
the rennet casein is relatively insoluble in alkalis so that it is 
out of the question for coated paper work. Acid caseins may 
be prepared by the action of any of the mineral, or the stronger 
organic acids; or the milk may be allowed to curdle spontane- 
ously from the formation of lactic acid. This latter procedure 
gives the so-called "self-soured" casein, while if acid has been 
used its name is usually attached to denote the method of 
preparation, as muriatic casein, sulphuric casein, etc. In this 
country acid is generally added to the skim milk, in South 
America much is made by self-souring, while in Europe both 
processes are used. 

Commercial casein is prepared from milk which has been 
freed as much as possible from fat by means of cream separa- 
tors. This skimmed milk is warmed to 49 to 50 C, the acid 
is added and when the curd has settled the whey is drawn off. 
The curd is then washed by hot water, drained on racks or 
boards, shredded, spread on wire bottom trays and dried in a 
current of warm air. The dried curd is then ground to any 
desired degree of fineness. If a high grade product is to be 
made great care must be taken that the wet curd is not kept 
so long that it has a chance to decompose or mould and the 
drying temperature must be closely regulated, since if it goes 
too high the casein becomes orange-brown and difficultly soluble. 
The kind of acid used also exerts a considerable influence on the 
character of the product; that made with muriatic acid gives 



334 



COATED PAPERS 



thick solutions which tend to foam and to become jelly-like on 
cooling, the self-soured produces thinner solutions which, on 
cooling, retain their fluidity to a notable extent, while that made 
by means of sulphuric acid occupies an intermediate position. 
The green curd from any of these methods can be used to good 
advantage in preparing the solutions for coating, but owing to 
its poor keeping qualities it is only obtainable locally. 

The nitrogen in pure casein has been found by various in- 
vestigators to range from 15.12 to 15.74 per cent, hence the per- 
centage of nitrogen found in any sample multiplied by the aver- 
age factor of 6.48 will give the percentage of ash-, fat-, and 
moisture-free casein. Commercial caseins have been found to 
contain about 13 per cent of nitrogen on an average so that the 
factor to convert percentage of nitrogen into commercial casein 
would be X 7-69. 

The results of examinations of samples of casein from both 
German and American markets are given below and show the 
variations to be expected in good commercial material. The 
German samples were tested by Hopfner and Burmeister, 1 while 
the American samples were analyzed in the author's laboratory. 





German 


American 




Max. 


Min. 


Avg. 


Max. 


Min. 


Avg. 


Per cent 

Moisture 

Fat 

Ash 

Nitrogen on total sample 

NaOH to neutralize to litmus .... 


10.50 
2 .06 
4-95 

13-55 


7.27 
O.23 

3-53 

12.52 


9-23 

0.85 

4.07 

12.99 


12.3 
9-9 

4-5' 

'3-83 


5-4 

trace 

1 .0 

1.30 


9-65 
3-68 
3-29 

2.51 



The specific gravity of commercial casein as received ranges 
from 1. 3 1 to 1.34 and the weight per cubic foot is 38.6 lbs. if 
run loosely into the container or 47.8 if tamped. 

The moisture in casein has been found to vary with the 
humidity of the surrounding atmosphere as is shown by the 
results of tests on two standard commercial samples. 

1 Chem. Ztg., 36, 19 12, 1053. 



CASEIN 



335 



Per cent humidity 


Moisture in 


Sample 1 


Sample 2 


40.6 

47-5 
52-7 
62.2 


7.27 
8.27 

9 13 

10.53 


7 .20 

8.06 

8.99 

10 -S3 



This explains why a sample of casein containing 12 to 14 
per cent of moisture when received will, if spread out in a thin 
layer, lose weight very rapidly at first until the moisture is 
reduced to 7 to 8 per cent and then will gain or lose in weight 
according to atmospheric conditions. 

Soluble caseins which were formerly on the market in large 
quantities, and are still met with occasionally, are merely mix- 
tures of ground casein and some alkali as. borax, soda ash, etc. 
An analysis of a representative sample gave the following results: 

Per cent 

Moisture 12. 2 

Casein (free from fat, ash, and moisture) 67. 1 

Soda ash, Na2C03 8.6 

Borax, Na 2 B 4 07, 10 H 2 3.1 

Fat 1.3 

Ash insoluble in water 9-3 

101. 6 

Such caseins are easy to handle but they are likely to keep 
poorly as the alkali may absorb water and act destructively on 
the casein, thus impairing its solubility and decreasing its 
strength. They also limit the user to the kind of alkali already 
mixed with the casein and do not permit its proper adjustment 
to the work in hand. A third point against them is that a 
cheap alkali is paid for at the price of casein so that the user 
can make quite a saving by buying both the alkali and the 
casein separately and mixing them himself in the proportions 
he desires. 

Casein is essentially of an acid nature and hence requires 
treatment with an alkali to bring it into solution. It forms two 



336 COATED PAPERS 

series of salts, those neutral to phenolphthalein being called 
basic casemates, while those neutral to litmus are known as 
neutral casemates. The casemates of sodium, potassium, lith- 
ium and ammonia are readily soluble, those of calcium, barium 
and strontium are much less so while those of the heavy metals 
are insoluble. 

The alkalis which have been proposed as solvents are am- 
monia and ammonium carbonate, and hydroxide, carbonate, 
silicate, borate, sulphite, and phosphates of sodium. Of these 
ammonia and the carbonate, borate and phosphates of sodium 
are the ones most frequently used while caustic soda is generally 
avoided because of its drastic action if used in excess. If care 
is used caustic soda is one of the best solvents, being cheap, 
quick in its action, and giving as good solutions as the more 
expensive solvents. The relative amounts of these alkalis re- 
quired to give a neutral. solution vary with the different caseins 
as the following figures from a large number of tests made with 
high-grade commercial solvents will show 

1 lb. borax, Na 2 B 4 07 • 10 H 2 

= 0.1736 — 0.2330 lb. NaOH average 0.2020 

= 1.062 — 1. 1 59 lb. Na 3 P0 4 - 12 H 2 average 1.130 

= 1. 1 58 — 1.872 lb. Na 2 HP0 4 - 12 H 2 average 1.419 

In the case of the phosphates the reaction evidently ceases 
when dihydrogen sodium phosphate is formed and this supposi- 
tion is confirmed by the fact that the latter salt has no appre- 
ciable solvent action even when used to the extent of 50 per cent 
of the weight of the casein. 

Practical application of these solvents brings out certain 
marked differences; ammonia is one of the quickest solvents 
and is especially useful in dissolving the last traces of the casein, 
the phosphates give thinner solutions especially with muriatic 
caseins, while borax is a reliable general solvent for most work 
but cannot be used with satin white. In any case a consider- 
able excess is to be avoided as it is wasteful, darkens the color 
and with most caseins causes a very marked thickening of the 



CASEIN 337 

solution. The full strength of a casein is developed if the 
alkali used is sufficient to give a solution neutral to litmus and 
while a moderate excess does not cause loss of strength, this 
does take place if a large excess is used, particularly if the heat- 
ing is prolonged. The amount of alkali required to give a 
neutral solution varies greatly with different caseins ; with borax 
the range may be as great as from 7 to 18 per cent. A diffi- 
cultly soluble casein may be improved by soaking it in 10 parts 
of water acidulated with acetic acid and then washing. This 
improves its solubility and reduces the amount of alkali re- 
quired. 

In very many caseins there is a small amount of insoluble 
matter which generally takes the form of white flakes resembling 
skins or envelopes from which the casein has been dissolved. 
In some cases these will dissolve on the addition of more alkali, 
but usually it is impossible to ehminate them in this way. They 
are light but bulky so that they appear to be present in large 
amount while in reality the percentage is very small, the worst 
sample which has been noticed containing only 1.64 per cent by 
weight. Under the microscope the great majority of these white 
flakes are found to consist of the hyphae of moulds so the old 
theory that they were particles of albumen precipitated by 
overheating of the milk is untenable. Additional proof of their 
nature has been obtained by moistening casein and allowing it 
to mould, then drying and grinding it to its original fineness. 
Four samples thus treated showed white flakes amounting to 
15 to 80 times those originally present and all had the same 
microscopic appearance as those present before moulding. These 
flakes cause trouble by working up into the brushes of the coat- 
ing machines and after they have collected in quantity, dropping 
off onto the paper thus making spots which sometimes stick to 
the calender rolls and break the paper. They also cause the 
brushes to work "dead" and not spread the coating well. These 
flakes, as well as all other undissolved foreign matter or casein, 
can be easily and completely removed by centrifugal clarifica- 
tion of the casein solution and the good portion of a casein 



338 COATED PAPERS 

which is dirty or partially insoluble can thus be obtained in fit 
condition to use. 

Solutions of casein are very liable to become spoiled, especially 
in the summer months, and such solutions cannot be used both 
because of their extremely bad odor and because the strength 
of the casein is very largely destroyed. Many substances have 
been proposed as preservatives for casein solutions, among them 
camphor, essential oils, salicylates, benzoates, hexamethylene 
tetramine, etc., but few of them are worth the added expense. 
The proper selection of alkalis has a large influence on the rate 
of spoiling, borax acting as a good preservative, while ammonia, 
phosphates or caustic soda permit rapid spoiling. Tests on the 
same casein with different solvents gave spoiled solutions in 
forty-eight hours when ammonia, caustic soda, or trisodium 
phosphates were used while if borax was employed the solution 
was good at the end of 16 days. Other experiments proved 
that 3 to 4 per cent of borax on the weight of the casein was 
sufficient, when mixed with other alkalis, to preserve the solu- 
tion as long as it would ever be necessary under normal working 
conditions, provided ordinary care was employed in keeping 
the tanks and mixers clean. For this reason it is a wise pre- 
caution to use a small amount of borax in preparing casein 
solutions. 

Another substance which acts as a preservative but which is 
used primarily as a waterproofing agent is formaldehyde. This 
is obtained commercially as a strong aqueous solution of the gas 
and should always be diluted with about ten times its volume 
of water before adding to the coating mixture. Over 2 per cent 
of the strong solution, based on the weight of the casein, will 
cause thickening while i| to 2 per cent can be added safely if it 
is well diluted and stirred in. This amount is sufficient to make 
the coating waterproof or washable, while even smaller quanti- 
ties produce very noticeable waterproofing effects. When small 
amounts of formaldehyde are used the waterproofing is slight at 
first but gradually develops so that paper which has been stored 
several weeks will show better results than when first made. 



TESTING CASEIN 339 

Many other substances are capable of rendering casein insol- 
uble but as most of them cause curdling or thickening of the 
casein solution they cannot be applied when the coating is spread. 
If casein coated paper is moistened with solutions of salts of iron, 
lead, copper, aluminum, magnesium, zinc, etc., the casein is 
rendered insoluble to such an extent that the paper may be 
safely washed. The use of any of these materials means putting 
the paper through one more process and as the desired properties 
can be more cheaply attained by formaldehyde none of them are 
now employed; they do, however, possess possibilities worthy of 
future investigation. 

Under normal conditions of storage caseins are apt to become 
infested with worms, the larvae of either moths or beetles, and 
the deterioration thus caused is very marked. Caseins affected 
in this way require less alkali to give neutral solutions and in some 
cases may lose as much as 50 per cent of their original strength 
in one year. The period of greatest deterioration is found to be 
in the summer, when the worms are most active, while in winter 
very little change takes place. Obviously the best conditions 
for lengthy storage would nearly approach those of cold storage 
plants. 

The tests which may be applied to casein are of two general 
classes, chemical analyses for certain constituents as moisture, 
ash, fat, or nitrogen and empirical tests to show certain proper- 
ties as solubility, strength, and alkali required. 

Moisture may be determined by drying in a thin layer at ioo° 
to 105 C. for about two and a half hours, cooling, and weighing 
in a closed vessel to prevent reabsorption of moisture. All 
caseins are not equally sensitive to heat but none have been 
found which, under these conditions, suffer decomposition which 
is serious enough to cause any appreciable error. In fact most 
caseins may safely be heated much longer at this temperature, or 
even as high as 115 C, without vitiating the results. 

The ash in casein may be determined by burning 2 to 3 grams 
in a silica dish; platinum should not be used because of the 
presence of phosphates which might be reduced and injure the 



340 COATED PAPERS 

platinum. In some cases the ash is gray and infusible while in 
others it melts to a clear, glassy mass. Rennet casein burns out 
readily and gives a high ash, while acid caseins are much harder 
to ignite free from carbon. 

Fat may be estimated by extracting the finely ground sample 
in a Soxhlet apparatus with ether and petroleum ether, evapora- 
ting the solvent, and drying and weighing the fat. A more 
accurate and rapid method is as follows: Soak 2 grams casein in 
6 c.c. water in a small beaker and after about half an hour add 
with constant stirring 9 c.c. of concentrated sulphuric acid (sp. 
gr. 1.84). Pour the solution into a Babcock skim milk bottle and 
wash out the beaker with 5 c.c. water and 5 c.c. H 2 S0 4 . Fill to 
the base of the neck with dilute sulphuric acid (4 c.c. water and 
5 c.c cone. H2SO4) and whirl in the Babcock centrifugal five 
minutes. Fill with dilute acid, whirl two minutes and while 
still hot read the fat on the graduated neck. The reading mul- 
tiplied by nine gives the percentage of fat in the casein. The 
secret of this method is in getting the concentration of the acid 
just right since if it is too strong the fat will char while if it is 
too weak the casein will not all be in solution and a reading will 
be impossible. 

Nitrogen is best determined by the usual Kjeldahl method. 
The factors for converting this to casein have been given above. 

These chemical analyses, while giving information as to the 
purity of the sample in question, do not show how it will work in 
practice, whether it is completely soluble, how much alkali it will 
require, whether the solution will be thin or thick, or whether 
the casein has good adhesive strength. For the manufacturer 
of coated paper these points are far more important than the 
chemical data and while such tests are for the most part com- 
parative they are quite simple to carry out and are sufficiently 
accurate for practical purposes. 

The alkali required, the consistency of the solution, and its 
completeness may be determined at one operation as follows: 
Soak 50 grams of the finely ground casein in 200 c.c. of water in a 
weighed No. 3 breaker for about half an hour then add a weighed 



TESTING CASEIN 



341 



amount of the solvent and heat on the steam bath with constant 
stirring. The amount of solvent should be less than will be 
required to give a neutral solution and the kind is immaterial so 
long as it is capable of being accurately measured; borax and triso- 
dium phosphate are very satisfactory or a standard caustic soda 
solution may be added from a burette in place of weighing the 
dry solvent. When the alkali added has all been used up test 
the solution by dipping in it a moistened piece of blue litmus 
paper. If the reaction is acid add more alkali and repeat the 
heating on the steam bath. This operation should be continued 
until the solution reacts neutral to litmus, which will be when it 
turns red litmus slightly blue and blue litmus slightly red. If at 
this stage the solution is not complete it is well to add more alkali 
and see if this excess will bring into solution all of that which is 
insoluble at the neutral point. This test indicates the minimum 
amount of alkali which can be used with the casein in question, 
shows whether it is good enough to use without clarifying the 
solution and by the consistency of the solution tells the expe- 
rienced man much as to the kind of alkali to use and the manner 
of running it on his coaters. The test is of such a nature that, 
so far as the consistency of the solution and its completeness go, 
it does not lend itself readily to numerical expression. For this 
reason the interpretation of the test requires experience and this 
cannot be imparted by words. 

The strength of a casein or the amount of clay which a given 
weight of casein will hold on the surface of the paper is best deter- 
mined by a method approximating actual coating operations. 
The apparatus is simple; a porcelain cup (without a handle), 
a brass plate, a steel scraper so shaped that a thin coating of the 
clay and casein may be applied to a sheet of paper, a copper stirrer 
flattened and bent at one. end so that the contents of the cup 
may be thoroughly worked over, and a set of scales capable of 
weighing down to 0.1 gram. One hundred grams of clay, pre- 
viously dried at ioo° C, are weighed out into the cup and soaked 
up with 70 c.c. water. The casein solution which was prepared 
in the solubility test is so adjusted, by evaporating or adding 



342 COATED PAPERS 

water, that each gram of dry casein is equivalent to 5 grams of 
solution. The clay and water are now worked over with the 
copper stirrer, the whole balanced up on the scales, 30 grams of 
casein solution added and the mass stirred until homogeneous. 
A sheet of paper is then laid on the brass plate, a little of this 
coating mixture placed on one end and a thin but even coating 
applied by means of the scraper. What coating mixture remains 
on the scraper is returned to the cup which is again balanced 
up, 5 grams more casein solution added and another sheet spread. 
This is repeated until the dry casein used amounts to 12 grams 
per 100 grams of clay. The coated sheets, which are marked from 
6 to 12, according to the amount of casein, are allowed to dry 
and then by looking through the sheets places of uniform thick- 
ness are selected and marked on each. Short pieces of high grade 
sealing wax are then melted on one end, either in a gas name or 
on the surface of a steam heated box, and applied to the marked 
places with a firm pressure. They are allowed to become thor- 
oughly cold and are then removed from the paper by a steady 
vertical pull. If enough casein is present the surface of the wax 
will be covered with fibres to the very edge, if too little has been 
used the coating comes away from the paper without pulling off 
any fibre, while there is usually an intermediate case in which 
the center of the wax shows fibre and the edges clay only; this 
would be considered just on the line between weak and strong. 

This is an excellent comparative test but it does not show the 
actual amount which can be used practically, but for several 
reasons indicates a higher strength than the same casein shows 
on a large scale. It will be found, however, that if this test shows 
one lot to be weaker than another it will be necessary to use more 
of the former than the latter when it is put on the coaters. The 
test is also influenced by the kind of clay, thickness of coating, 
nature of paper, etc., so that it is necessary to use standard 
materials in carrying it out. This means that, while it gives very 
valuable comparative results in the hands of experienced persons 
and under standard conditions, it is not safe to compare results 
obtained in different laboratories. 



STARCH 343 

Albumen. Both blood- and egg-albumen are similar in some 
respects to casein yet differ from it by losing their solubility 
if heated to about 75 C, while casein may be treated with boiling 
water and still be soluble when the correct proportions of alkali 
are used. 

Solutions of either of these may be prepared by stirring the 
albumen into warm water to which a little spirits of ammonia 
has been added. The temperature should not be over 20 C. and 
the stirring must be frequent enough to prevent the albumen 
from collecting and sticking on the bottom of the container. 
Other substances are also used as assistants in dissolving albumen, 
as borax, magnesium sulphate, etc. The strength of albumen is 
very nearly equal to that of casein, 24 to 28 parts of albumen 
doing the work of 22 to 24 parts of casein. 

Coatings prepared with albumen are not rendered so water- 
proof by formaldehyde as are casein coatings; they may, however, 
be made washable by heating, preferably in the presence of steam. 
Mixtures of casein and albumen when treated in this way give 
washable coatings which are good for chromo and leather papers 
because of their capacity to absorb printing ink. While under 
certain conditions albumen gives a higher finish to paper than 
does casein yet it is seldom used because of its high price and in 
many cases its disagreeable odor. 

Starch. As an adhesive for coated paper work starch has 
many good points; it is clean, of good color, without odor, non- 
nitrogenous and hence not liable to putrefactive decomposition, 
has good strength and is cheap. The different starches, such as 
corn, wheat, cassava, potato, etc., have quite distinct character- 
istics yet all are sufficiently alike so that they may be discussed 
as a class. 

The simplest way to prepare an adhesive from starch is to stir 
the dry starch into 8 to 15 times its weight of water and heat 
to the boiling point. Different starches vary as to the temper- 
ature at which they gelatinize and the thickness of the paste they 
produce but with reasonable amounts of water all are too thick 
to use on the ordinary coating machine. This difficulty may be 



344 COATED PAPERS 

overcome by modifying the starch by chemical treatment so that 
it cooks thinner while at the same time losing nothing in strength 
but in many cases actually gaining in adhesive properties. Such 
modified starches may be produced by treatment with acids, 
acid salts, oxidizing agents, etc., under very varied conditions 
and the patents taken out along such lines are almost innumer- 
able. The products of these treatments resemble the original 
starches in appearance but as stated give much thinner solutions 
and also have, according to their method of preparation, minor 
differences which sometimes cause trouble on the coaters. 

A well made modified starch for coated paper work should 
give a light colored, thin solution when one part of starch is 
boiled with four parts of water. This solution should not thicken 
too much on cooling or at least should thin down to its original 
consistency on reheating. While there are many such products 
only a few give satisfactory mixtures with clay as most are lack- 
ing in the property which glue and casein possess of making the 
clay into a very fluid suspension. The lack of this quality 
causes the coating mixture to work "dead" or draggy and the 
paper is apt to show brush marks, or if these results are to be 
avoided so much water has to be added that the drying lines are 
overtaxed and the capacity of the machine is reduced. The 
strength of starch has been found to be slightly less than that of 
casein so that about 20 to 25 lbs. are required to do the work of 
18 to 20 lbs. of casein. 

Coated papers prepared with starch do not take such a high, 
glossy finish as casein coated papers, partly because of the larger 
amount of adhesive used and partly because of the nature of the 
starch itself. Even the addition of considerable amounts of wax 
does not enable it to take so good a finish as casein coated paper. 
This does not prevent half tones taking well on it for its surface 
is sufficiently smooth and even to print well. A characteristic 
feature of starch coated paper is the porosity or absorbent power 
of the surface. This seems to be greater than with glue or casein 
coatings so that the printing ink tends to sink in rather more and 
the resulting cut, especially with color work, is slightly dull. 



CLAY 345 

This trouble can be overcome by a proper adjustment of the ink 
but at present it is delaying the general introduction of starch 
coating, though otherwise the paper works well, running well on 
the presses, permitting rapid work and requiring no slip-sheeting. 

Miscellaneous Adhesives. Other materials have been pro- 
posed from time to time as assistants to, or substitutes for, casein 
and among these may be mentioned glutin, viscose, shellac, 
algse, vegetable gums, mucilages, etc. While these may be, and 
probably are, used in small quantities or for special purposes, as 
for instance shellac in the manufacture of imitation leather 
papers, their employment is by no means general and it is not 
probable that they will ever seriously compete with casein. 

Clay The nature and properties of clay have been discussed 
in the chapter on fillers and the methods of testing which are 
given there apply equally well to coating clays. The principal 
differences between filler and coating clays are in color and fine- 
ness, the coating grades being whiter and finer and containing less 
grit. These differences are not by any means along hard and 
fast lines since the higher grade filler clays are sometimes used for 
coating, while for certain kinds of high class book papers, good 
grades of coating clay are used in the beating engines. The 
presence of grit in clay for coating is more serious than in a filler 
since it is sure to appear on the surface of the paper where it inter- 
feres with the finish and may even cause trouble in printing, 
especially in lithographing. In this process it is said to etch the 
stones or plates so that the portions which should remain white 
are not entirely ink resistant thus permitting the ink to be trans- 
ferred to the paper when it is not desired and giving tinted or 
mottled backgrounds. 

The fineness of the clay has a large influence on the finish which 
the paper will take on calendering, the finer the particles of the 
clay the higher the gloss which is imparted. Unfortunately the 
amount of casein, or other adhesive, required increases quite 
rapidly as the size of the clay particles decreases so that the gain 
in finish due to a fine clay is in part offset by the effect of more 
adhesive. Unexpected or unknown changes in the fineness of 



346 COATED PAPERS 

the clays used are without doubt responsible for some of the cases 
of weak coating, especially when the amount of casein used is 
kept as near the minimum as possible. 

With ordinary clays from 15 to 18 parts of casein are required 
for 100 parts of clay and with this casein any of the ordinary 
solvents as borax, soda ash, ammonia or mixtures of these 
solvents may be used with good results. 

Blanc Fixe and Barytes. Both of these are chemically barium 
sulphate, BaS0 4 ; blanc fixe being prepared by precipitation 
while barytes is the natural mineral ground and bolted to any 
desired degree of fineness. The best grades of blanc fixe are 
prepared from witherite (BaC0 3 ) by dissolving in muriatic acid, 
filtering and precipitating with sulphuric acid. The precipitate 
is washed practically free from acid and put on the market 
either dry or as a paste containing 25 to 30 per cent of moisture. 
Cheaper grades of blanc fixe are produced as by-products in the 
manufacture of hydrogen peroxide, etc., and appear to be only 
slightly inferior to that from witherite in color and cleanliness. 
Under the microscope blanc fixe is seen to consist of extremely 
fine crystals, which are very uniform in size. If large irregular 
shaped pieces are present it may be taken as an indication of 
adulteration with barytes or of very careless handling of the 
solutions before precipitation. The grit in blanc fixe, as 
determined by the flotation test described in the chapter on 
fillers, should not exceed 0.2 to 0.3 per cent and it should con- 
sist almost entirely of small lamps of the blanc fixe itself which 
have not broken down during the test. This test also will show 
the presence of barytes though not its amount. The reaction of 
blanc fixe varies commercially from neutral to decidedly acid; 
both appear to give equally good results under ordinary working 
conditions as the acid is neutralized by the excess of alkali in the 
casein. 

Barytes, being a ground mineral, gives much larger amounts 
of grit than blanc fixe, the flotation test showing from 8 to 15 per 
cent for different commercial grades. Its particles are much 
coarser and more variable in size than those of blanc fixe, and 



SATIN WHITE 



347 



it is usually quite inferior to the latter in color. For these reasons 
it should not be used in the highest class of papers. 

Blanc fixe is one of the whitest of the minerals used in coating 
paper and can be used in the very best of products. It does not 
take such a high finish as clay or satin white and is especially 
serviceable in making dull finish coateds since it has less tendency 
to scratch than clay or satin white. Since barium sulphate is 
practically insoluble it cannot react with casein solutions so that 
almost any solvent can be used in preparing the latter. Both 
blanc fixe and barytes require much less casein than does clay and 
both tend to settle out of the coating mixture more rapidly than 
clay on account of their high specific gravity. 

Satin White. This material consists essentially of calcium 
sulphate and aluminum hydrate, formed by the interaction of 
slaked lime and aluminum sulphate; 3 Ca (OH) 2 + Al 2 (S0 4 ) 3 
= 3 CaS0 4 + Al 2 (OH) 6 . The alum used may be potash or 
ammonia, or aluminum sulphate itself may be used, and the 
character of the resulting product depends very largely on which 
is employed. The slaked lime is frequently used in excess and 
the amount of this excess together with the quality of the lime 
has a very great influence on the working properties and color 
of the product. The following analyses of two commercial sam- 
ples of satin white show its approximate composition after being 
dried at ioo° C. 



Sulphur trioxide, SO 

Alumina, AI2O3 

Total lime, CaO 

Loss on ignition .... 



No. 1 


No. 2 


Per cent 


Per cen 


28.9 


29 -3 


13 -9 


12.3 


39- 1 


39-7 


17-5 


18. 5 


99-4 


99.8 



Both these samples contained 24 to 26 per cent of free lime 
while other samples tested for this substance have shown that 
it may run as high as 30 per cent, or the satin white may even 
be perfectly neutral. 



348 COATED PAPERS 

In the commercial preparation of satin white the slaked lime 
is mixed with alum solution, or in some cases the undissolved 
alum, and after sufficient agitation to insure a uniform reaction 
the paste is diluted, strained through fine wire gauze, 130 to 140 
mesh, and run into a filter press where it is washed with clear 
water. The resulting paste containing about 30 per cent of bone 
dry material is the satin white of commerce. When a standard 
method of manufacture has once been established it should be 
strictly adhered to, since changes in the kind or proportions of 
the ingredients may cause differences which may not appear in 
the analysis yet which will cause serious trouble in the coating 
room. In fact it cannot be safely predicted from the analysis 
how a lot will work and the only sure way is to give it a trial on a 
practical scale. 

The properties imparted to coated paper by satin white are 
high gloss on calendering and clear white color. Because of the 
presence of aluminum hydrate the coating becomes rather dense 
and brittle so that papers with much satin white have rather 
poor folding qualities; this is especially true with very heavily 
coated papers. 

The amount of casein required to hold a given amount of satin 
white is much greater than for the same amount of clay, prob- 
ably in most cases nearly one and one half times as much. Special 
precautions have to be used in mixing the two or the result is 
a thick, curdled mass which cannot be spread. In order to avoid 
this difficulty the casein solution may be prepared with an ex- 
cess of soda ash or with a mixture of sodium phosphate and 
ammonia and the satin white should be mixed with a little 
ammonia before the casein is added. When phosphates are 
present with satin white heating causes thickening so that hot 
casein solution should not be mixed with satin white, nor 
should the mixture be heated. For working with this material 
temperatures of 30 C. or below are desirable. If these precau- 
tions are observed very little trouble will be encountered. 

Accessories. Under this heading may be mentioned those 
materials which are used in small amounts or for special pur- 



ACCESSORIES 349 

poses and which do not form an essential part of the coating 
itself. 

Soaps and waxes are added for the purpose of improving the 
finish obtained on calendering. Among those used may be men- 
tioned, beeswax, carnauba wax, stearic acid, paraffin, Japan wax, 
white soap, lard oil, etc. Many different recipes are used for 
mixing the ingredients but most of them are suspensions or 
emulsions of one or more substances in a soapy medium. Japan 
wax has the property of saponifying very readily and is quite 
generally used to hold the other materials in suspension. As an 
example of this type the following formula may be cited; to 
about 250 gals, of hot water add 50 lbs. each of Japan wax, para- 
ffin and stearic acid and then 22 lbs. borax and a little ammonia. 
When stirred until the waxes are melted this forms a creamy white 
permanent emulsion which is ready to use in the coating mixture. 

While it is undoubtedly true that such materials assist in 
obtaining the high finish on glace papers repeated trials have 
demonstrated that they are of doubtful value for the ordinary 
grades of coated papers and it has been proved that at times 
some of them may be responsible for poor results in printing. 

Closely connected with this class of materials are those added 
to prevent undue frothing of the coating mixture; in fact some 
of the substances sold to improve the finish are also claimed to 
reduce the froth. Anti-frothing substances may have widely 
different characteristics as for instance wood alcohol, Turkey red 
oil, fusel oil, skim milk, and gasoline. Probably no one of these 
will work in every case as froth varies in its character and cause 
but it is believed that a little gasoline added to the frothing mix- 
ture from time to time will give the best results. This sub- 
stance should be used with great caution on account of the danger 
of fire. 

For softening the coating and increasing its pliability glycerine 
is frequently recommended. Its beneficial effect is supposed to 
be due to its hygroscopic nature but tests have shown that com- 
mercial glycerines absorb very little moisture from the air so that 
the increase in weight of the paper would be practically only that 



350 COATED PAPERS 

of the glycerine added. Tests by a large manufacturer indicate 
that amounts up to 2 per cent of the weight of dry clay in the 
coating have practically no effect on the folding properties of the 
coated paper and if 5 per cent is used the printing qualities of the 
paper are seriously injured. 

The glycerine substitutes, mostly invert sugars, are even less 
hygroscopic than glycerine itself and hence would have even less 
effect. The use of any of these substances is therefore of doubt- 
ful advantage and their use is not to be recommended. 



CHAPTER XIII 
WATER 

Water which is pure, in the sense that it contains no foreign 
matter of any kind, is never found in nature, so that from the 
manufacturing standpoint, as well as from that of sanitation, 
water must be considered with reference to the amount and 
kind of the impurities which it contains. These may include 
solid, liquid or gaseous substances and they may be either in 
suspension or solution. Both mineral, or inorganic substances, 
and organic materials may be present, and the latter may be 
derived from decaying vegetation or from minute living organ- 
isms. Some of these substances may have a great influence on 
the quality of the paper, while others, which are harmless for 
this purpose, are decidedly bad if used in boilers. The quality 
of the available water supply is therefore a vital consideration 
in connection with the manufacture of paper. 

The comparative readiness with which the quality of the 
water affects that of the paper is still further emphasized by a 
consideration of the very large volumes necessary for the vari- 
ous manufacturing operations. Griffin and Little 1 estimate the 
amount required in making a ton of paper at 50,000 to 200,000 
gals., or about 200 to 800 times the weight of the paper pro- 
duced. Others have estimated that in American fine paper 
mills, making linens, bonds and ledgers from rag stock, the 
water used amounts to 1000 gals, per pound of dry paper made. 2 
Reliable data for water consumption are rarely available and 
no generally applicable figures can be given because its use 
depends so largely on local conditions, as purity, quantity avail- 

1 Chemistry of Paper Making, p. 330 (1894* 

2 Paper: June 21, 1916, p. 12. 

3Si 



352 WATER 

able, cost of pumping, necessity for filtration, reuse of back- 
water, etc. In some cases it may be necessary to purify the 
waste waters in order to avoid stream pollution and this tends 
to reduce the amount of water used. Considering these enor- 
mous volumes, and the fact that the paper stock forms a very 
effective filter, the result of very small amounts of injurious sub- 
stances may be easily imagined. Compared with this problem 
that of the boiler-house supply for steam raising is relatively 
unimportant. 

Waters may be broadly classified as (i) rain, (2) surface and 
(3) ground waters. Rain water, if properly collected, is the 
purest form of natural water, though it always contains gases 
and impurities from roofs, products of combustion, etc. Be- 
cause of the relatively small amounts available it is of no prac- 
tical importance as a paper making supply. Surface waters 
include those of brooks, rivers, ponds and lakes. These waters 
pick up impurities of various kinds according to the nature of 
the soils over which they flow and they are also contaminated 
by mineral substances derived from springs which discharge 
into them. They generally contain less mineral matter but 
more organic matter than ground waters, and, particularly in 
the case of river waters, are likely to vary greatly in composi- 
tion at different periods of the year. Suspended matter is usu- 
ally present in greater or less amount and in the case of swamp 
waters there is usually a yellowish color due to the peaty soil 
over which the water has passed. Waters of this type are 
likely to contain plant and animal life which may impart con- 
siderable color to them. Ground waters are those which have 
percolated through a considerable depth of soil and the under- 
lying porous strata. Such waters, derived from springs and 
deep wells, are usually clear and colorless but they contain 
more dissolved mineral matter than do surface waters. 

Soft waters are those which contain little of those mineral 
substances which are capable of decomposing soap, while hard 
waters are those which possess this property to a marked de- 
gree. The most common cause of hardness is the presence of 



. WATER 353 

lime salts, either the sulphate or carbonate, the latter being 
much the more general. The salts of magnesium have an even 
greater effect than those of calcium but they are not so often 
present. The sulphates of both calcium and magnesium are 
soluble in pure water but the carbonates require the presence 
of carbon dioxide to enable them to dissolve as bicarbonates. 
The necessary carbon dioxide is derived from the air, from the 
decay of vegetable matter or from subterranean sources. Bicar- 
bonates form what is termed "temporary hardness" since on 
boiling the carbon dioxide is driven off, causing the precipita- 
tion of calcium carbonate and the softening of the water. Sul- 
phates cause "permanent hardness" since they are not affected 
by boiling. 

Soft water is said to be desirable for the washing of stock 
because it has a greater solvent power than hard water. If the 
latter is employed for washing sulphite fibre there is a tendency 
for insoluble calcium resinates to be deposited on the fibre, 
thus rendering the product unnecessarily hard to bleach, while 
in the soda process the lime salts may be precipitated as car- 
bonate or sulphate and carry down coloring matters with the 
same result. 1 Water which is very hard because of the pres- 
ence of calcium bicarbonate may also be injurious to sizing, 
though the presence of calcium sulphate is harmless. For other 
purposes in paper making as in the boiling of either sulphite, 
soda or rag stock, or in bleaching, or furnishing an engine, the 
importance of soft water is greatly overestimated since the 
materials employed will immediately harden the softest water. 

In making colored papers the quality of the water may affect 
the results obtained. Carbonates cause precipitation of the 
salts of iron, tin and aluminum, which are sometimes used as 
mordants, and reduce their effectiveness. Sulphates have little 
or no action. Neither carbonate nor sulphate will cause trouble 
when using acid colors as the amount of acid used far outweighs 
any alkali present in the water. Iron in the water dulls almost 
all mordant colors. It is also very injurious in the manufac- 

1 Beveridge: Paper, Oct. 30, 19 18. 



354 



WATER 



ture of photographic paper, particularly if it is present in such 
form that it may deposit in the pipes, reservoirs, etc., as such 
sludge may break away at times and cause endless trouble. 1 

The most important quality of water, from a paper making 
point of view, is its color. The purest natural waters are clear 
and colorless when examined in comparatively thin layers, while 
in large masses they have a bluish tint. Surface waters on the 
other hand show all variations in color from colorless, through 
yellowish and reddish tints, to the deep brown of swamp water. 
This color is due largely to decaying vegetable matter and 
where the decay has proceeded far the color is very permanent 
in character. The color derived from plant growths, princi- 
pally algse, is usually most pronounced in the .summer months. 
They are green or bluish green, require light for their develop- 
ment and thrive best in ponds or reservoirs where there is little 
movement to the water. These lower forms of plant life are 
very sensitive to copper sulphate and a treatment with a very 
small amount of this material is sufficient to destroy them. 
This method is often used, even in the case of a water supply for 
drinking purposes. 

At times the color of a water is greatly affected by the sus- 
pended matter which it carries; this is a very variable factor, 
its greatest effect appearing when heavy rains have washed 
much finely divided soil into the streams. Soluble mineral 
matter has, as a rule, little effect on the color, even the soluble 
salts of iron are seldom present in sufficient concentration to 
cause any perceptible color. Trouble is caused, however, when 
for any reason these iron salts are precipitated as hydroxide. 

Practically all waters, especially surface waters, consume small 
quantities of bleaching powder, the amount depending upon 
the source of the water. In most cases the loss of bleach from 
this cause is slight but if much organic matter is present, as in 
swamp waters or those largely contaminated with trade wastes 
or sewage, the loss may be appreciable. Griffin and Little 2 

1 Anon: Paper, Jan. i, 1919. 

2 Chemistry of Paper Making, p. 333 (1894). 



BOILER SCALE 355 

give the bleach consumed by three waters as 1.77, 1.16 and 3.87 
grains per gallon but do not state the source of the water or the 
conditions of the test. 

Water which is to be used for boiler purposes should gener- 
ally be soft and free from suspended matter, for substances 
either in solution or suspension will accumulate and form mud 
or scale. Such a deposit may be hard and dense or loose and 
porous according to the substances present. Dense scale is the 
more serious and water which causes it should either be avoided 
or treated in some way. Such a scale causes a large loss of fuel 
by preventing the transfer of heat to the water and when it is 
of any considerable thickness there is danger of overheating the 
boiler locally with consequent damage to the tubes or plates. 
Hardness, however, is not always an indication of scale forming 
power for both calcium chloride and magnesium sulphate make 
water hard but do not form scale. 

One of the most frequent causes of scale is calcium carbonate. 
This is present as bicarbonate but at the temperature of the 
boiler is again broken down into calcium carbonate and carbon 
dioxide. This same reaction takes place with magnesium bicar- 
bonate and if both are present in the water they will be found 
together in the scale. The precipitated carbonates are at first 
loose and powdery but if the boiler is blown off without cooling 
the flues, the precipitate is likely to bake into a dense, hard 
scale. Under these conditions the magnesium appears in the 
scale as hydroxide. Calcium carbonate is not so likely to bake 
onto the plates as the magnesium salt. The following analysis x 
shows the general characteristics of a carbonate scale, though 
the relative proportions are likely to vary quite widely in 
different samples. 

Per cent p er cen t 

Carbonate of lime 75. 85 Silica 7. 66 

Sulphate of lime 3 . 68 Oxides of iron and alumina 2. 96 

Hydrate of magnesia 2. 56 Organic matter 3. 64 



Chloride of sodium o. 45 Moisture . 



20 



1 Griffin and Little: Chemistry of Paper Making, p. 334 (1894). 



356 



WATER 



If the hardness of a water is due to calcium sulphate no pre- 
cipitation takes place until the solution becomes saturated due 
to concentration; then a crystalline scale deposits. This is at 
first CaS0 4 • 2 H 2 0, but it begins to lose its water of crystal- 
lization at about 260 F. and becomes more insoluble. These 
actions tend to produce a hard scale which may accumulate to 
a considerable thickness. 

A certain amount of scale may be formed in the boilers even 
when the water is soft, though the quantity is almost never 
enough to be serious. The following analyses show the com- 
position of a soft water which proved excellent for boiler pur- 
poses and also of the scale which formed during its use. 

Water * 



Constituents 



Parts per 
million 



Per cent of 
dry matter 



Silica (Si02) 

Iron (Fe) 

Calcium (Ca) 

Magnesium (Mg) 

Sodium and potassium (Na + K) . 

Carbonate radicle (C0 3 ) 

Bicarbonate radicle (HCO3) 

Sulphate radicle (SCU) 

Nitrate radicle (NO3) 

Chlorine (CI) 

Total suspended solids 

Total dissolved solids 



3-8 

0.04 
3-2 
0.6 
4.2 
0.0 
14.0 
3-6 
°-5 
1.6 

7-4 
25.0 



i5-5 

0.2 

i3- 1 

2.4 

17. 1 

28.5 



14.7 
2 .0 
6-5 



Scale 



Moisture and organic matter . 

Silica (SiO-2) 

Ferric oxide (Fe 2 3 ) 

Alumina (A1 2 3 ) 

Calcium oxide (CaO) 

Magnesium oxide (MgO) 

Carbon dioxide (CO2) 

Sulphur trioxide (SO3) 



Per cent 

17.16 

35-64 

4-32 

4.28 

30.97 
5-59 
1 .40 

Q-9 2 
100.28 



Analysis by U. S. Geological Survey. 



Water Softening. Many so-called "boiler compounds" have 
been proposed for use in the prevention of scale and while some 



WATER SOFTENING 357 

may work well under certain conditions, none are of universal 
application and many are useless or even injurious. If the 
water is bad enough so that a "boiler compound" seems de- 
sirable, it is in most cases preferable to give it a preliminary 
softening treatment. 

For waters containing the bicarbonates of calcium and mag- 
nesium the method most generally employed is that of Clark, 
which consists in adding slaked lime to react according to the 
equation : 

CaH 2 (C0 3 ) 2 + Ca(OH) 2 = 2 CaC0 3 + 2 H 2 

The lime is added either as lime water or milk of lime, the 
former being preferable because it is more easy to control. 
This treatment removes all the bicarbonate as well as the added 
lime. 

This method was originally applied in large tanks where the 
water could remain quiescent for a considerable time. The 
lime water was added in such an amount that, after thorough 
mixing, the water gave a yellow or brown color with silver 
nitrate, then more water was added until the silver nitrate 
test gave no color. This test should always be applied in order 
to make sure that an excess or deficiency of lime is not caused 
by variation in the water supply. Temporary hardness of 
course is all that is removed, and even that not completely, as 
a little calcium carbonate remains in solution and magnesium 
bicarbonate is not so completely removed as that of calcium. 
Salts of iron and some organic matter are also removed. 

Various modifications of this process have been tried out in 
the attempt to shorten, or do away with, the time required for 
settling. The Porter-Clark process employs a filter press for 
the removal of the precipitate. Gaillet and Huet cause the 
water to take a zig-zag course to promote sedimentation and 
often use both lime and caustic soda to remove both temporary 
and permanent hardness according to the reactions 

CaH 2 (C0 3 ) 2 + 2 NaOH = CaC0 3 + Na 2 C0 3 + 2 H 2 0, 
CaS0 4 + Na 2 C0 3 = CaC0 3 + Na 2 S0 4 . 



358 WATER 

The Archbutt-Deeley process blows air through the treated 
water after mixing it with the sludge from a previous precipi- 
tation. This hastens the sedimentation so that the clear water 
may be drawn from the top by a floating arm. Other proposed 
modifications employ barium hydroxide, sodium oxalate, mag- 
nesium hydroxide, etc. The latter is not always to be recom- 
mended as it may result in the formation of magnesium chloride 
and consequent corrosion of the boiler. 

An entirely different process is the so-called permutite pro- 
cess. Permutite is an artificial zeolite formed by fusing together 
silica, alumina or china clay, and sodium carbonate. On ex- 
traction with water a crystalline body is obtained of the approxi- 
mate composition, Si0 2 , 46; A1 2 3 , 22; Na 2 0, 13.6; H 2 0, 18.4. 
Filtration of water through this material removes the calcium 
and magnesium thus: 

Na 2 Al 2 Si 2 8 + CaC0 3 = Na 2 C0 3 + CaAl 2 Si 2 8 , 
Na 2 Al 2 Si 2 8 + CaS0 4 = Na 2 S0 4 + CaAl 2 Si 2 8 . 

It is claimed that the whole of the hardness is removed and 
that the calcium and magnesium zeolites formed can be recon- 
verted into the original permutite by treating with a strong 
solution of salt. A manganese permutite can also be used for 
the removal of iron. 

Filtration. The principal action in filtering water is that of 
straining to remove suspended mineral and vegetable matter. 
It is, however, much more complex than a mere straining since 
the water undergoes chemical and biological changes, particu- 
larly in slow sand-filtration. Among these changes oxidation 
is one of the chief, due to the fact that in passing through porous 
earth an enormous surface is exposed. In natural filtration, 
during the transformation of surface into ground waters, this 
action may proceed so far that all the organic matter originally 
present is oxidized leaving the water clear and colorless. In 
continuous mechanical filtration no such oxidation takes place and 
the removal of organic matter has to be secured by other. means. 

Many forms of mechanical filters have been devised, some 



WATER ANALYSIS 359 

working by gravity and some under pressure. With all of them 
some provision is made for cleaning the filtering medium, which 
is usually sand, either by reversing the flow of water, by me- 
chanical agitation with rakes, by compressed air or some other 
means. The frequency of such cleaning depends on the quality 
of the water, and if this varies much, due to the time of year, 
storms, etc., the intervals between cleaning will also vary. If 
the stream from which the water is drawn is contaminated with 
fibre, sawdust or other coarse mechanical impurities the effi- 
ciency of the filters may be greatly increased by first running 
the water supply over a revolving screen similar to the moulds 
of a wet machine. 

Water may be filtered directly, in which case only suspended 
matter will be removed, or it may first be treated with a little 
alum. The slight alkalinity of most waters causes the precipi- 
tation of hydrated alumina which on standing for some time 
collects in flocks of appreciable size, gathers together finely 
divided suspended matter and at the same time takes out much 
of the organic coloring matter. The precipitate forms a film 
over the filtering medium and aids in removing bacteria and 
other minute organisms. If much loam or silt is present a 
little lime is sometimes added before the alum to insure a suffi- 
ciently bulky precipitate. The amount of alum necessary de- 
pends on the hardness of the water. It is customary to add 
it mechanically by some sort of device controlled by the flow 
of the raw water so that the proportion added may be the same 
at all times. After the addition of the alum it is desirable that 
the water remain for thirty minutes to an hour in a settling 
basin where heavy sediment may settle and the chemical reac- 
tion between the alum and the bases present in the water may 
take place. It is then ready to pass to the filter. 

Water Analysis. The following analytical methods have been 
taken in large part from "Standard Methods for the Examina- 
tion of Water and Sewage," J to which reference should be 
made if more complete details are desired. 

1 Am. Public Health Assn., Boston, 1917. 



360 WATER 

Sampling. Care must be taken that the sample is truly rep- 
resentative of the liquid to be analyzed. If for any reason 
variations are likely to occur, as for instance because of periodic 
contamination by trade waste, a sample obtained by mixing 
together several portions taken at different times is likely to 
be more representative than one taken all at one time. The 
amount required for the ordinary chemical, physical and micro- 
scopical analysis is not less than two liters, and for special tests 
larger quantities may be required. 

The samples should be collected in glass-stoppered bottles 
which have been previously cleaned with sulphuric acid and 
potassium bichromate or with alkaline permanganate, followed 
by a mixture of oxalic acid and sulphuric acid and by thorough 
rinsing and draining. The stoppers and necks of the bottles 
should be protected from dirt by tying cloth or thick paper 
over them. 

The time which may safely elapse between the collection of 
the sample and its analysis depends on the character of the 
sample and the tests to be made. No exact limits can be fixed 
but it is considered that the analysis should be begun within 
the following times. 





Physical and 
chemical analyses 


Microscopic 
examinations 


Ground waters 


Hours 
72 
48 
12 


Hours 
72 
24 


Fairly pure surface waters 


Polluted surface waters . . . 









In general the shorter the time elapsing between the collection 
of a sample and its analysis the more reliable will be the ana- 
lytical results. 

Turbidity. The turbidity of water is due to suspended mat- 
ter such as clay, silt, finely divided organic matter, microscopic 
organisms, etc. 

The standard for turbidity adopted by the United States 
Geological Survey, 1 is a water containing 100 parts per million 

1 F. D. West: Proc. 111. Water Supply Assoc, Vol. VI, pp. 49-51, 1914- 



COLOR 361 

of silica in such a state of fineness that a bright platinum wire 
1 mm. in diameter can just be seen when the centre of the wire 
is 100 mm. below the surface of the water and the eye of the 
observer is 1.2 meters above the wire. This observation should 
be made in the middle of the day, in the open air but not in 
sunlight, and in a vessel so large that the sides do not shut out 
the light so as to influence the results. The standard may be 
prepared by sifting dry Pear's "precipitated fuller's earth" 
through a 200-mesh sieve and suspending 1 gram of the mate- 
rial in 1 liter of distilled water. This has a turbidity of 1000 
but should be tested by diluting with nine times its volume of 
water and trying out with the platinum wire apparatus. If not 
exactly right it may be adjusted by adding more silica or more 
water. This method requires a rod with a platinum wire 1 mm. 
in diameter inserted in it 1 in. from one end and projecting 
from it at least 25 mm. Near the other end of the rod and 1.2 
meters from the wire is fixed a small ring, directly above which 
the observer places his eye when making the observation. This 
rod is graduated so that when lowered into the water to be 
tested, as far as the wire can be seen, the level of the water on 
the graduated scale indicates the turbidity. 

Turbidity may also be determined by the candle turbidi- 
meter, 1 which consists of graduated glass tubes with flat pol- 
ished bottoms, enclosed in a metal case. This is supported 
over an English standard candle so that the distance from the 
bottom of the tube to the top rim of the candle shall be 3 ins. 
The observation is made by pouring the sample of water into 
the tube until the image of the candle flame just disappears. 
This test should be carried out in a darkened room or with a 
black cloth over the head. An electric light may conveniently 
be substituted for the candle as it avoids any deposit of soot 
or moisture on the tubes. The calibration of the instrument 
may be made by means of the silica standards already mentioned. 

Color. The "true color" of water is that due to substances 
in solution while the "apparent color" is that of the original 

1 Tech. Quart., Vol. XIII, pp. 274-279, 1900. 



362 WATER 

unfiltered sample and includes also any color caused by sus- 
pended matter. 

A convenient standard for color 1 is prepared by dissolving 
1.246 grams of potassium platinic chloride (PtCl 4 • 2 KC1), con- 
taining 0.5 gram of platinum, and 1 gram crystallized Cobalt 
chloride (C0CI2 • 6 H 2 0), containing 0.25 gram of cobalt, in 
water with 100 c.c. concentrated hydrochloric acid and diluting 
to 1 liter with distilled water. This solution has a color of 500 
and by diluting in Nessler tubes standards of o, 5, 10, 15, 20, 
2 5> 3°> 35? 4°> 5°> 60 and 70 should be prepared. These tubes 
should be of such diameter that the graduation mark is 20 to 
25 cm. above the bottom and of such uniformity that the dis- 
tance from the bottom to the graduation of the longest tube 
shall not be more than 6 mm. greater than that of the shortest 
tube. The tubes should be protected from light and dust when 
not in use. 

The color of the sample is measured by filling a standard 
Nessler tube to the height equal to that in the standard and 
then comparing by looking vertically downward through the 
tubes upon a white surface placed at such an angle that light 
is reflected upward through the liquid. Water with a color 
greater than 70 should be diluted before testing, and water con- 
taining suspended matter should be filtered unless the apparent 
color is desired, in which case unfiltered water should be used. 

Nitrogen. This occurs in water in various forms as ammonia, 
nitrites, nitrates, etc., and its determination has been standard- 
ized by numerous methods. It is of very great importance 
when considering water from a sanitary standpoint, as its pres- 
ence in any appreciable quantity indicates pollution, but as it 
is of minor importance in the manufacturing operations of 
paper making the methods for its determination will not be 
discussed. 

Oxygen Consumed. This is determined by heating 100 c.c. 
of the water with 10 c.c. of dilute H 2 S0 4 and 10 c.c. of a stand- 
ard solution of potassium permanganate, adding 10 c.c. of a 

1 Am. Chem. J., Vol. XIV, pp. 300-310, 1892. 



SUSPENDED MATTER 363 

standard ammonium oxalate solution and titrating the excess 
with the permanganate. 

It is considered by some as an indication of the amount of 
carbonaceous matter present but where pollution, or contami- 
nation with trade wastes, has taken place it will also include 
such materials as nitrite nitrogen, ferrous iron, sulphides, etc. 

As a substitute for this determination it is suggested that a 
direct determination of the bleach consumed by the water under 
conditions of temperature and time similar to those of actual 
fibre bleaching operations would be of much more value to the 
paper maker. This can be carried out by adding a known vol- 
ume of a standard hypochlorite solution and after allowing it to 
stand for a definite time determining the amount remaining; 
the difference represents the amount consumed. 

Residue on Evaporation. Ignite and weigh a clean platinum 
dish, and measure into it 100 c.c. of the thoroughly shaken 
sample. Evaporate to dryness on the water bath, heat in an 
oven at 103 C. or 180 C. for one hour, cool in a desiccator 
and weigh. The increase in weight gives the total solids or 
residue on evaporation. The results should be expressed as 
parts per million and the temperature of drying should be given 
in the report. 

Fixed Residue. Ignite the total solids in the platinum dish 
at a low red heat. Cool, moisten the residue with a few drops 
of distilled water, dry in the oven, cool in a desiccator and 
weigh. For the greatest accuracy an electrically heated muffle 
furnace should be used. The loss on ignition is the difference 
between the total residue on evaporation and the fixed residue 
on evaporation. 

Suspended Matter. This may be determined directly by 
means of an asbestos lined Gooch crucible or indirectly by cal- 
culation from the difference between the total solids in filtered 
and unfiltered portions of the same sample. 

A test which gives valuable information regarding the paper 
making value of water is made by treating a definite volume of 
the water with enough dilute aluminum sulphate solution to 



364 WATER 

precipitate all coagulable matter. After allowing it to stand 
a sufficient time for coagulation to take place, it is filtered 
through a Gooch crucible or through a tared filter paper and 
the weight of the precipitate determined by difference after 
drying. The amount and character of the precipitate indicate 
whether the water will prove satisfactory without filtration or 
whether it will be necessary to treat it with alum and filter 
before using. 

Hardness. A water is said to be hard when it contains in 
solution mineral constituents, which form insoluble compounds 
with soap. The most accurate method of ascertaining total 
hardness is to calculate it from the amounts of calcium and 
magnesium found by analysis of the sample. If appreciable 
amounts of iron or other metals are present these must be 
included in the calculation. The total hardness expressed as 
CaC0 3 equals 2.5 Ca plus 4.1 Mg. 

Titration with standard soap solution is a method often em- 
ployed for determining total hardness, though in reality it 
merely measures the soap consuming power of the water. The 
soap solution is prepared by dissolving 100 grams of dry, white 
Castile soap in 1 liter of 80 per cent alcohol. After standing 
several days dilute 100 c.c. to 1 liter with 70 per cent alcohol 
and standardize against a solution of calcium chloride contain- 
ing the equivalent of 0.2 gram CaC0 3 per liter. This is done by 
placing 20 c.c. of calcium chloride solution in a 250-c.c. glass- 
stoppered bottle and diluting to 50 c.c. with distilled water 
which has been recently boiled and cooled. To this the soap 
solution is added from a burette, 0.2 to 0.3 c.c. at a time, shak- 
ing vigorously after each addition, until the lather remains 
unbroken for five minutes over the entire surface of the water 
while the bottle lies on its side. Repeat this test, using 15 c.c, 
10 c.c. and 5 c.c. of the calcium-chloride solution and finally 
distilled water alone, and from the results plot a curve showing 
the relation of various quantities of soap solution to correspond- 
ing quantities of calcium carbonate and hence to parts per 
million of hardness. 



IRON 365 

In testing water 50 c.c. of the sample are placed in the bottle 
and the test carried out exactly as in the standardization of the 
soap solution. If magnesium is present a false end point may- 
be obtained. To see if this is the case, read the burette when 
the end point has apparently been reached and then add 0.5 c.c. 
more of the soap solution. If the end point was caused by mag- 
nesium the lather will disappear and the titration must be 
continued until the true end point is reached. 

Temporary Hardness. Temporary hardness is due to mag- 
nesium or calcium carbonates which are held in solution as 
bicarbonates by dissolved carbon dioxide, and which are partly 
precipitated when the latter is driven off by boiling. It is most 
accurately estimated by determining the alkalinity by titration 
with N/50 acid, using methyl orange as indicator, both in the 
original water and again after boiling, cooling, making up to 
the original volume with boiled distilled water and filtering. 
The difference between the two titrations represents temporary 
hardness which would include iron bicarbonate. 

Alkalinity or Acidity. Alkalinity or acidity may be deter- 
mined by titration with N/50 acid or sodium carbonate re- 
spectively. Indicators for alkalinity include phenolphthalein, 
methyl orange, lacmoid and erythrosine while for total acidity 
phenolphthalein should be used. 

Chlorides. The chlorides in water are due to common salt, 
which may come from mineral deposits in the earth, from wind- 
borne ocean vapors or from sewage and trade wastes. 

It may be determined by titrating a measured volume of the 
water with standard silver nitrate, using chloride-free potassium 
chromate solution as indicator. This shows a faint reddish 
color when the end point is reached. If the water has a color 
greater than 30 it should be decolorized by shaking with a little 
washed aluminum hydroxide and allowing it to settle. The 
clear portion is then used for the test. The results should be 
expressed as parts per million of chlorine. 

Iron. Iron may be present in both the ferrous and ferric 
states. In ground waters it is usually in the ferrous condition 



366 WATER 

and combined with carbonic or sulphuric acid or with organic 
matter. After exposure to air it is frequently present as a col- 
loidal hydroxide. Silt-bearing waters often contain much iron 
in suspension, while waters contaminated with sewage effluents 
and manufacturing wastes contain various forms of iron of 
different degrees of solubility. 

The total iron present may be determined as follows: Evapo- 
rate ioo c.c. of the water to dryness and ignite at a low red 
heat. After cooling add 5 c.c. of concentrated hydrochloric 
acid, moisten the surface of the dish and warm two or three 
minutes, again moisten the inner surface of the dish with the 
acid and wash the solution into a 50-c.c. Nessler tube. Dilute 
to 50 c.c, add 3 drops of N/5 potassium permanganate solution 
and then add 5 c.c. of potassium sulphocyanide solution. Com- 
pare the color produced with that from solutions of known iron 
content similarly treated with sulphocyanide. 

The fixed residue from a previous determination may be dis- 
solved in hydrochloric acid, converted to sulphates by evapora- 
tion with sulphuric acid, and treated as in the modified Stokes 
and Cain method as applied to the analysis of alum. 

Manganese. The determination of manganese may be car- 
ried out colorimetrically if the water contains less than ten parts 
per million but if more than this amount is present it may be 
preferable to use a volumetric or gravimetric method. 

The amount of water used should contain not more than 0.2 
mg. of manganese. Add to it 2 c.c. of nitric acid (concentrated 
acid diluted with an equal volume of water), and boil down to 
50 c.c. Precipitate the chlorides with silver nitrate, being sure 
that a slight excess is used, and filter. Add about 0.5 gram 
ammonium persulphate crystals and warm the solution until 
the maximum permanganate color is developed, which usually 
takes about ten minutes. At the same time prepare standards 
containing 0.2, 0.4, 0.6 c.c, etc., of the standard manganous 
sulphate solution to about 50 c.c. and treat them in exactly 
the same way as the standard. Transfer sample and standards 
to Nessler tubes and compare the color at once. 



MANGANESE 367 

The standard manganous sulphate is prepared by dissolving 
0.288 gram of the purest potassium permanganate in about 
100 c.c. of distilled water, acidifying with sulphuric acid, boiling 
and just discharging the color with a dilute solution of oxalic 
acid. After cooling and diluting to 1 liter, 1 c.c. of the solution 
contains 0.1 mg. of manganese. 



CHAPTER XIV 
TESTING WOOD PULPS 

In the purchase of wood pulp it is very desirable to have some 
means of judging its quality, as otherwise the material obtained is 
quite likely to be entirely unsuited to the grade of paper being 
made. The usual crude tests, such as feeling of the sheet, tearing 
it and noting the length of fibre, biting the fibre to note its hard- 
ness, etc., at best give but a slight idea of its suitability for the 
work in question and if intelligent purchases are to be made 
more definite methods of testing must be devised. Accurate 
sampling and testing are also very essential in the case of moisture 
determinations, since pulp is purchased on a 10 per cent moisture 
basis and large sums of money are frequently at stake. 

The following methods are those which have been gradually 
worked out during years of experience but they are given as a 
working basis rather than as final and unalterable procedures, 
since it is certain that many of them are capable of considerable 
improvement. 

Moisture in Wood Pulp. Baled Pulp. The following is the 
official method of sampling and testing baled pulp as adopted by 
the American Paper and Pulp Association and the Association of 
American Wood Pulp Importers. 

"All tests must be made by a chemist duly authorized and 
approved by the joint committee representing the Association of 
American Wood Pulp Importers and the American Pulp and 
Paper Association on one side and the Scandinavian Wood Pulp 
Associations on the other side, and must be made strictly in 
accordance with the following instructions — otherwise the com- 
mittee reserves the right to withdraw the approval of any 
chemist at any time. 

368 



LOCATION OF BORINGS 



369 



"Before proceeding to the weighing and sampling the chemist 
must ascertain that not less than half of the parcel in question is 
available. 

" Number. Not less than 5 per cent, nor more than 10 per cent 
of the entire shipment, but not less than ten bales shall be sam- 
pled. Samples to be drawn only from sound and intact bales, 
from different sections of the entire shipment, and analyst shall 
be careful to observe that no unusual con- 
ditions prevail in the selection of the bales. 
The accurate weight of all bales sampled to 
be ascertained by sworn weigher before samp- 
ling, or, wherever sworn weigher is not avail- 
able, by a competent person who must make 
sworn affidavit that weights are correct, and 
no other bales than those weighed to be 
sampled, and whenever bales are numbered, 
the number is to be given in addition to the 
weight. - 

"Method of Sampling 

"Depth of Boring. The sample shall be 
taken by boring into a bale to a depth of 3 ins. 
(7.62 cm.) with a special auger which cuts 
a disk about 4 ins. (10.16 cm.) in diameter. 

"Selection of Disks. The disks shall be 
removed, and ten of them taken as a sample, FlG - 4°- Cutter for 
these to be selected as follows: Sampling Pulp 



1 disk 2nd sheet from the wrapper. 

2 disks 1 in. (2.5 cm.) deep. 

3 disks 2 in. (5.05 cm.) deep. 

4 disks 3 in. (7.62 cm.) deep. 



" Location of Borings. The holes to be bored shall be so located 
that in five successive bales they will represent a portion extend- 
ing diagonally across the bale. Each bale to be bored but once. 
The first hole to be bored at the corner, the edges of the cut being 



370 TESTING WOOD PULPS 

at a distance of one inch from the edge of the bale. The second 
cut shall then be made half way between the location of the first 
cut and the center of the bale, the third bale shall be cut at the 
center, the fourth bale half way between the center and the corner, 
and the fifth bale in the opposite corner in a position correspond- 
ing to the first. 

"All samples must be either weighed immediately after being 
drawn from the bales by accurate scales, or, when this is imprac- 
ticable, must be put into airtight vessels, made of metal or glass, 
with ground-glass or metal stoppers, and due care must be used 
in the transportation of such samples until they can be properly 
weighed at the laboratory of the chemists. The entire bulk of 
samples selected from the bales must be dried out for the test. 
The temperature in the drying oven shall not exceed 21 2° F. 

"Chemists must have proper and adequate equipment for 
weighing and sampling the bales, and for the weighing and 
drying of samples. 

"All sampling of pulp must be done by or supervised by the 
approved chemist personally, or by his bona fide assistants — 
each chemist to file with the committee a complete list of his 
bona fide assistants who will do the sampling, such list to have 
the approval of the committee. The chemist will be held respon- 
sible for the correct sampling by his approved assistants. The 
committee shall at any time have the privilege of investigating 
the sampling done by chemists or their assistants. 

" Every test certificate shall clearly state the name of the person 
who did the sampling. 

"The test certificates hereafter shall be uniform and in accord- 
ance with forms to be approved by the committee, a sample draft 
of which will be furnished by the committee to each chemist." 

This procedure can also be applied to rolls, making the first 
boring 1 in. from the end, the second half way between the end 
and the middle, the third at the middle, and so on. 

This method of testing is the quickest of any which has been 
proposed and it leaves the bales or rolls in good shape to be 
stored or shipped but it is not necessarily the most accurate. In 



LAP PULP 371 

the opinion of the author it favors the seller of the pulp since the 
percentage of moisture decreases more rapidly on the outside 
than in the centre and the loss in the weight of the bale does not 
keep pace with the decrease in the percentage of moisture as 
shown by the sample taken. This is particularly true of bales 
put aside for a retest and stored in a comparatively dry place for 
several weeks ; such re tests therefore nearly always show a greater 
net weight of air dry pulp than do the original tests. 

The quarter-sheet method of sampling consists essentially of 
opening up the bales and taking a quarter of a sheet from different 
parts of the bale in such a way that the combined samples would 
cover the entire area of the bale. It is variously applied by dif- 
ferent workers; some take two quarter-sheets from each bale, 
others more, the extreme being ten quarter-sheets starting with 
the second sheet from the wrapper and spacing the others equally 
between the second sheet and the centre of the bale. On the 
whole it is believed that the quarter-sheet method is more accu- 
rate than the disc method already described but that it is unprac- 
tical because of the large amount of time and labor involved and 
because it leaves the bales in no condition for storage or further 
shipment. 

Lap Pulp. The methods of testing pulp for moisture have 
been exhaustively investigated by the Technical Section of the 
Canadian Pulp and Paper Association. 1 For lap pulp from ordi- 
nary wet machines or Rogers wet machines they tentatively 
recommend taking a strip 3 ins. wide clear across the sheet and 
to the full thickness of the sheet. Such a sample should be. 
taken for each 2000 lbs. of wet stock in the shipment. Tests 
by this method in comparison with the entire sheets dried out 
prove that the two methods give practically identical results and 
that the strip method is therefore accurate. 

For hydraulic pressed pulp they recommend the wedge system 
as proposed by Woodruff. 2 They have proved that this method 
gives more accurate results than the strip method in which 

1 Slack: Pulp Paper Mag. Can., XVII, 1919, 265. 

2 Woodruff: Paper, Oct. 3, 1917, p. 86. 



372 TESTING WOOD PULPS 

2-in. strips are cut from the centre of the lap to the outer edge, 
the cut portions forming a cross for each four samples. In the 
wedge system for hydraulic pulp a template is employed to mark 
the laps. This template has an angle of 9 degs. and at its apex 
is attached a disc divided into forty parts. This disc is placed at 
the centre of the lap and the wedge marked out by a pencil along 
the edges of the template. The lap is put one side and the next 
marked in a like manner, but moving the wedge of the template 
to the second position on the disc. Forty laps are thus marked, 
giving a total sample equivalent to one entire lap. The marked 
laps are then taken to a circular saw and the wedges cut out. 
These wedges may be split in halves if it is necessary to reduce 
the bulk of the sample. 

Strength or Beating Test. This method of testing was first 
described by the writer in 191 5 x and was the outcome of an 
attempt to demonstrate experimentally the variations in the 
strength of sheets made from different sulphite fibres after they 
had been given the same beating treatment. The method first 
proposed is as follows : 

The fibre to be tested is allowed to become air dry and two lots 
of 50 grams each are then weighed out. One of these is soaked up 
in 1000 c.c. of water and reduced to pulp by rubbing with the 
hands; it is then rinsed into a small pebble mill with just 1000 
c.c. more water. The mill is now closed and allowed to revolve 
at 60 revolutions per minute for exactly an hour, at the end 
of which time the entire contents are emptied upon a §-in. mesh 
sieve and the pulp washed off the stones into a pan placed 
beneath the sieve. The pan is then filled to a definite mark — 
27 liters total contents, and four sheets are made on a hand 
mould, taking two dips for each sheet and reversing the hand 
mould between dips so that the sheets may be of uniform thick- 
ness on the two edges. After pressing between felts in a copying 
press the sheets are air dried and are then tested for strength 
with an Ashcroft tester. Five bursting tests are made on each 
sheet along one of the diagonals and the average of the twenty 

1 Paper, Nov. 10, 19 15. 



STRENGTH OR BEATING TEST 



373 



tests taken as representing the beaten strength of the sample. 
If it is desired to compare the strength before and after beating 
the second sample of 50 grams is broken up into a pulp as before 
and made into sheets from the same volume of water as in the 
case of the beaten pulp. 

This method has been slightly modified * by the Committee on 
Sulphite Pulp of the Technical Association of the Pulp and Paper 
Industry but the changes they propose are largely to shorten the 
time required and do not alter any of the essential features of the 
test as originally proposed. 

Many factors influence the results of this test and in order to 
get concordant results careful control is necessary. This does not 
lessen the value of the method but it means that intelligent super- 
vision is essential if the best information is to be derived. Some 
of the vital factors will be briefly mentioned. 

The size of the pebble mill as well as its volume and charge of 
pebbles must be carefully considered. Two mills of the same 
make often vary enough in size and capacity so that very different 
beating effects are obtained. The only satisfactory way seems to 
be to assume one to be right and adjust the charge of pebbles, 
fibre and water in the other so that the same strength test will 
be given by the beaten fibre. If the results in two plants are to 
be directly comparable it will of course be necessary to stand- 
ardize their pebble mills on the same lots of fibre. This is not a 
serious inconvenience and is not found to detract much from 
the value of the test since in most cases comparative results only 
are wanted. 

The proportions of fibre and water must be closely adhered 
to, as comparatively slight variations cause appreciable differ- 
ences in the bursting strength. This is also true of the time of 
beating, which should be regulated with care and not allowed to 
vary more than a minute or two. 

Factors having minor influence on the tests are the temperature 
of the water in the pebble mill and the relative humidity of the 

1 Paper, Nov. 8, 1916. 



374 TESTING WOOD PULPS 

atmosphere when the bursting tests are made. For ordinary rou- 
tine tests consideration of these factors may be neglected. 

A variable having great influence in many cases is that of the 
moisture in the pulp when taken for the test. Wet pulp will 
not give the same test as it will after being air dried. Experi- 
ments on one lot of pulp showed that the beaten strength was 
highest in the wet lap and decreased as the moisture diminished; 
the change from 70 to 5 per cent moisture reduced the bursting 
strength from 64.7 lbs. to 40 lbs. This change cannot be reversed 
by wetting dry pulp, which indicates the reason for air drying all 
samples before testing so that all may be on the same basis. For 
the most accurate work it would be very desirable to dry all 
samples at a constant humidity since this would insure more 
concordant results. One of the changes which it was proposed 
to make in the original method was to press the samples of wet 
pulp to a constant moisture and use this pulp as a basis for the 
test. This shortens the time required but it does not permit com- 
parison of the wet pulp with one received in the air dry condition. 

A point of very great importance is the manner of forming the 
sheets to be tested. If a hand mould is used the weight of the 
sheets varies considerably depending on whether the fibre is 
"free" or "greasy" after beating. It has been proposed to get 
around this difficulty by calculating the breaking test per unit 
weight of sheet but this is not an entirely satisfactory method. 
All such variations can be eliminated by using some form of sheet 
making machine in which a constant volume of stock is used 
and none is lost by overflowing the edges as happens with the 
deckle of the hand mould. 

Different methods of employing this test may be used; the 
original idea was to beat for a fixed time and note the differences 
in the strength developed, but Hatch l has adopted the modifica- 
tion of beating a number of samples for different lengths of time 
in order to see what maximum strength would be developed and 
the time necessary for its production. 

For other interesting data relating to the beating test reference 

1 Paper, Oct. 3, 1917. 



COLOR COMPARISON OF BLEACHED PULPS 375 

is made to the work of Mansfield and Stephenson l and of 
Sutermeister. 2 

This method of testing gives satisfactory results with sulphite, 
soda, and sulphate pulps but does not appear suitable for ground 
wood since the latter is not affected by the beating treatment to 
nearly so great an extent as the others. 

Color Comparison of Bleached Pulps. The method outlined 
here has been taken, with slight modifications, from the report 
of the Committee on Sulphite Pulp of the Technical Association 
of the Pulp and Paper Industry. 3 

The grading of the shade of a piece of bleached pulp usually 
leads to very uncertain results. Two pieces of pulp, which under 
certain conditions of light appear identical in shade, under 
different light conditions appear to be very different in shade. 
Very often bleached pulp which is satisfactory in shade under 
artificial light, appears quite yellow in daylight. Again, different 
pieces of the same pulp often appear to be of different shade, 
when graded together under identical light conditions. This 
latter phenomenon can be due only to one cause: differences in 
the surfaces of the two pieces of the same pulp. The problem 
to be solved therefore appeared to be twofold. 

1. To devise some means of obtaining constant illumination 
conditions; and this illumination to be of such a quality that 
slight differences in shade could be easily distinguished. 

2. To devise a means whereby 

(a) the surface of different pulps could be made the 

same, or 

(b) the effects of different surfaces of different pulps 

could be minimized. 

Many so called daylight lamps were tried, including both the 
bulb and arc types. Finally the arc type of color comparator 
made by the General Electric Company was adopted as giving 

1 Pulp Paper Mag. Can., Oct. 1, 1916. 

2 Paper, Dec. n, 1918. 

3 Paper, Nov. 8, 1916, 19, No. 9. 



37 6 TESTING WOOD PULPS 

the most constant artificial light of all those tried out and a 
light whereby one could most easily distinguish small differences 
of shade. 

The procedure adopted consists in attaching six disks of the 
pulp to be tested to the front of six wheels of varying degrees of 
whiteness. The wheels and pulp are then revolved at high speed 
(2,500 revolutions per minute) and the operator judges to which 
of the standardized color wheels the pulp is nearest in shade. 
The shade of pulp is then declared to be that of the wheel to which 
it is nearest in color. The test being made always under the 
same conditions of illumination both variable factors of light and 
pulp surface are rendered constant and thereby the remaining 
variable, the actual shade of pulp, can be easily determined. 

Description of Apparatus 

1. Cutting Press. The disks of pulp are cut with a press and 
dies of the type F0 2 , made by the Ferracute Machine Company, 
of Bridgeton, N. J. The dies are so arranged that a disk 3! ins. 
in diameter is cut with a f in. hole in the center, at one operation. 

2. Revolving Disk Machine. Fig. 41 gives details of the con- 
struction of this apparatus. The method of preparing the differ- 
ently shaded wheels is as follows: Different combinations of 
plaster of Paris, magnesia and chromate of potash are made into 
a paste with water, this paste poured into the brass wheel, allowed 
to set and then planed down to a smooth surface. 

It is recognized, of course, that one fixed standard of color 
shade is not applicable as a standard to all kinds of pulp. For 
example: bleached pulp when run from a drying machine has a 
radically different shade from the same pulp run through a wet 
machine and hydraulically pressed. Yet both pulps on being 
made into paper would give identical color shades to the paper. 
Hence, it is necessary to employ different color mixtures on the 
revolving disk machine for different types of pulp. Again the 
standard of pulp color shade demanded by some manufacturers 
of paper is entirely different from that of other manufacturers. 
Hence it is not possible to recommend a formula applicable to 





(377) 




u 



(378) 



DAYLIGHT LAMPS 



379 



all cases. The formula given here is applicable to bleached 
drier pulp and the color 95, as named in this report, when applied 
to this product is satisfactory to the great majority of paper 
manufacturers in this country. 

The different wheels are numbered as follows, reading from 
left to right: 

100, 95, 90, 85, 80, 75. 

The formulas are as follows : 



No. of wheel 


Water 


Plaster of 
Paris 


Chromate of 
potash 


Magnesia, 
powdered 


IOO 


120 


107 


O.O 


20 


95 


120 


107 


O.0245 


20 


9° 


120 


214 


O.1490 


O 


85 


120 


214 


O.4660 


O 


80 


120 


214 


O.6120 


O 


75 


120 


214 


0.7770 


O 



The plaster of Paris and magnesia are first thoroughly mixed 
together, then the water added and the paste thoroughly stirred 
up and poured into the wheel. 

When pouring the wheels containing the chromate, the latter 
is first dissolved in the water, the solution added to the plaster of 
Paris, the whole thoroughly stirred up and poured into the wheel. 

After pouring, the wheels are allowed to set forty-eight hours 
and then revolved by means of the motor, and turned down 
smooth with a sharp-edged cold chisel and finished with fine 
sandpaper. 

A sewing machine belt was tried out to drive the machine, but 
a satisfactory fastener could not be found which at the speed 
employed would not pull out after a short time. It was found 
that I in. rope with a spliced joint stands up very well. 

3. Daylight Lamps. Two of these, manufactured by the 
General Electric Company, are used. They are known as their 
direct current multiple color matching outfits. The whole 
apparatus, of course, is placed in a dark room, where no light 
rays can penetrate to interfere with the light of the lamps. 



380 TESTING WOOD PULPS 

This method of testing is a noteworthy attempt at putting 
the designation of color on a numerical basis in a practical way 
and it is in successful operation in several mills. The equipment 
is however rather expensive, and if several grades of pulp, such 
as soda poplar, sulphite spruce, and sulphate pine, are to be 
examined a large number of standard discs must be kept on 
hand and the preparation of the filling for such discs is by no 
means easy and is often quite unsatisfactory. 

It is the belief of the author that fully as reliable comparisons 
can be made by using hand mould sheets as explained under 
"Bleaching Qualities." It is of course desirable that such com- 
parisons should be made under a "daylight lamp" in a dark 
room but if this is not available a north light should be used and 
tests made at as nearly as possible the same time each day. 

Bleaching Qualities. The method used in determining the 
bleach required by a sample of fibre depends on the point of 
view of the observer and should in general be made to conform as 
closely as possible to actual operations in the plant in question. 
The method preferred by the author is as follows : Two 50-gram 
samples of the fibre are weighed out and at the same time a small 
sample is taken for a moisture test. From this moisture test 
it is possible to calculate the air dry fibre (10 per cent moisture) 
corresponding to the 50-gram samples and upon this air dry 
weight the figures for bleach are based. One of the samples is 
now broken up in a little water in a 6-in. by 8-in. battery jar until 
a uniform pulp is obtained and this is then diluted to about two 
liters with water. From a solution of bleaching powder, whose 
strength has previously been determined, a volume is measured 
out which corresponds to the percentage of bleach which it is 
estimated the fibre will require. This is added to the jar of pulp 
and the contents kept agitated and at about 35 to 40 C. until 
the bleach is just exhausted. The fibre is then thrown upon 
a screen of 70-mesh wire and washed with a heavy stream of 
water to remove the bleach residues and break up any knots or 
balls of fibre which may have formed. The pulp is next made 
into hand mould sheets which are dried on a small steam heated 



BLEACHING QUALITIES 381 

cylinder and compared with sheets of pulp of the standard color. 
If the color is found to be much different from the standard a 
second test is made using more or less bleach as the first test 
indicates. 

Since bleached fibre slowly changes in color it is quite essential 
to obtain some permanent standard but so far efforts along this 
line have not been entirely successful. Plates of dull porcelain 
have been suggested but the difference in surface texture between 
the porcelain and the fibre sheets would probably render the 
comparison of their colors quite unsatisfactory. Attempts have 
also been made to use slabs of plaster of Paris tinted to the right 
shade and given the desired surface texture by pressing between 
felts. Great difficulty was experienced in getting just the right 
color in such slabs. The most practical method seems to be to 
cut out a large number of samples from the same lot of unbleached 
pulp and -determine with great care the amount of bleach required 
to give the standard white color. After this is determined one 
sample is bleached each month, the sheets made therefrom serv- 
ing as the standard for the month following. 

In plants where practically this same method of bleaching is 
carried out the above scheme of testing is found to give results 
in very close agreement with those of actual practice. In other 
plants where an excess of bleach is added and the residual bleach 
washed out after the color is brought up to the desired shade a 
method of testing employing these same principles should be 
used. In such tests a known amount of bleach is added and 
that remaining at the end of the test is determined by analysis; 
from these data the per cent used by the fibre may be calculated. 
This method of testing is quicker than the one first given but it 
is necessary to compare the colors of the bleached fibres in the 
wet state before the yellow products of the bleaching action have 
been removed. 

Bichter x has suggested a method of testing sulphite fibres 
which depends on the comparison of the colors developed on treat- 
ing samples of unbleached fibre with nitric acid. Weighed sam- 

1 E. Richter: Proc. Eighth Int. Cong. Appd. Chem. 



382 TESTING WOOD PULPS 

pies of the fibre to be tested, and also of one whose bleaching 
properties are known, are treated with 13 per cent nitric acid 
solution for about an hour; portions of the acid are then drawn 
off and compared in a colorimeter of any standard construction. 
Knowing the bleach required by one fibre it is possible to esti- 
mate that necessary to produce the same color in the other 
sample. This method is quick and may possibly be reasonably 
accurate with fibres cooked under nearly the same conditions but 
with samples from a number of different mills it proved to be 
only approximate, some of the results being as much as 10 to 15 
per cent higher or lower than the figures obtained by actual bleach- 
ing trials. Moreover it does not appear to be applicable to 
soda and sulphate fibres, at least when a sulphite fibre is used as 
a standard for comparison. 

Loss in Weight on Bleaching. This test, taken in connection 
with the bleaching test, throws considerable light on the value of 
a pulp, since it shows what loss in weight will be suffered by the 
fibre because of the oxidizing and solvent action of the bleach, 
apart from the mechanical loss in the bleaching process, which 
should be practically the same for all fibres. The method is as 
follows: 

Weigh out two samples of about 2 grams each and determine 
the moisture in one by drying to constant weight at ioo° to 105 . 
The second sample is broken up to a pulp in a little water by 
rubbing between the thumb and fingers and the pulp transferred 
to a small flask. This procedure requires care and skill but after 
a little experience it can be done with no loss of fibre. Bleach 
solution is now added from a burette, the amount being regulated 
to give the percentage which the bleaching test proved would 
give the standard white color in the sample being tested. The 
flask is now kept at about 35 to 40 until the bleach is exhausted, 
when the fibre is transferred to a Gooch crucible, washed very 
thoroughly with hot water, dried and weighed. The difference 
in the bone dry weight of the unbleached and bleached fibre, 
which shows the loss due to the chemical action of the bleach, 
may conveniently be expressed as percentage Of the former. 



NATURE AND AMOUNT OF DIRT 383 

Sedimentation Test. This test is one which has not yet been 
standardized but which has been applied to the study of pulps 
by many different observers most of whom used home-made ap- 
paratus of some sort. The principle of the test is that the longer 
the fibres have been beaten, or in the case of ground wood 
the finer it is ground, the more slowly it will part with its water. 
The general method of making the test is to place a known 
amount of fibre, reduced to a uniform pulp in a definite volume 
of water, in some sort of receptacle with a perforated bottom 
through which the water can drain and on which the fibre settles 
to form a mat. A valve below the false bottom prevents the 
escape of the water until the desired time and makes it possible 
to record the time of outflow. In Fishburn and Weber's appara- 
tus 1 the receptacle is a graduated glass cylinder and the test 
consists in" noting the time required for the water level to drop 
9! ins. In the Riegler-Schopper 2 tester, Fig. 42, the water drain- 
ing from the stock falls into a chamber having two discharge out- 
lets of different dimensions and at different levels. The amount 
of water issuing from the large orifice, which is at the higher 
level, gives an indication of the degree of beating or the natural 
slowness or quickness of the stock. The smaller opening, which 
discharges under a practically constant head, acts as a sort of 
automatic cut-off and by taking care of the last slow drainage 
from the test sample it makes the differences in the results more 
marked. 

A test of this nature, using a long tube as a sedimentation 
chamber, has been used in testing sulphite pulps and it is 
claimed 3 that it shows very marked differences between long 
and short fibred stocks. 

Nature and Amount of Dirt. The dirt in a sample of pulp 
can be successfully investigated if a sheet of it is wet and examined 
by transmitted light. A convenient outfit consists of a box 
painted white inside and fitted with two or more electric light 

1 Fishburn and Weber: Paper, Oct. 11, 1916, 13. 

2 U. S. Pat. 1,193,613, Aug. 8, 1916. Paper, Aug. 30, 1916. 

3 "Snowshoe": Pulp Paper Mag. Can., Sept. 5, 1918, XVI, 793. 



384 



TESTING WOOD PULPS 











I 


<» 


=T 








(% 








kj) 


ts 


m 










{ 



NATURE AND AMOUNT OF DIRT 385 

bulbs. The top of the box consists of a glass plate upon which 
the pulp rests. This box may be of any convenient size but the 
sample of pulp should completely cover its top so that no glare 
from the lights enters the observer's eyes. If a box is made to 
take a sheet 6\ X 8 ins. and the dirt is counted on both sides a 
simple multiplication by 2 gives the dirt count per 100 sq. ins., 
which has been found a satisfactory method of expressing the 
results. The sheets to be examined should be of nearly uniform 
thickness so that the count may be on practically the same 
quantity of pulp in every case. If desired the dry sheets can be 
weighed before testing and in this way the dirt count can be placed 
on a weight basis. If the material in question is not received 
in the form of sheets it may be made into sheets on a hand mould 
before examination. It will be found convenient to dry these 
completely and again wet them before examination; this will 
enable the wet sheets to be handled with much less trouble than 
if they are taken direct from the hand mould in which case they 
tear so readily that they are extremely difficult to turn over. In 
making this test it is well to dig out with a needle the specks of 
dirt which are not directly on the surface, since particles which 
appear to be dirt, will, in some cases, prove to be small rolls of 
fibre. It is also desirable to record the results under at least 
two headings, dirt and shives, and in some special cases it is even 
well to classify them in such groups as cinders, bark, iron rust, 
etc., as this will often enable the chief cause of the trouble to be 
located. 

The results obtained in this test depend almost entirely on the 
opinion of the observer as to what constitutes dirt and since the 
opinion of different observers often varies widely it is plain that 
the tests should all be made by one person in order to avoid the 
personal factor. Records of this nature are valuable in showing 
whether the product of any plant is being kept up to standard and 
they are also helpful in selecting pulps in the market when 
purchases are in question. 



CHAPTER XV 
PAPER TESTING 

In the following chapter are given the methods in common 
use in the testing of paper, together with some of the more 
unusual tests which are occasionally called for. It has been 
attempted to give these methods concisely but in sufficient 
detail to enable them to be carried out without difficulty by 
any technically-trained man who has had some experience in 
the paper industry. It should not be forgotten, however, that 
the intelligent interpretation of the results depends in many 
cases upon the judgment of the observer and that good judg- 
ment can only be replaced to a slight extent by even the most 
detailed directions. 

The essential features of a number of these tests have been 
taken from the report of the Committee on Paper Testing of the 
Technical Association, 1 to which acknowledgement is hereby 
made, and the student is referred to this report for more com- 
plete details of many of the methods. There are also included 
a considerable number of tests which are not mentioned in this 
report but which practical experience has shown to be of value 
in the study of paper. For a more detailed study of the factors 
influencing many of these tests reference should also be made 
to Herzberg's "Papierprufung," 2 where the subject is exhaust- 
ively treated. The methods of testing are grouped under three 
heads: microscopical examinations, physical testing, and chemi- 
cal analysis. 

Microscopical Examinations 

The microscope offers practically the only means for deter- 
mining the kinds of fibres and the relative proportions of each 

1 Paper XXV, 693, 739, 777, 831 and 877, Dec. 10, 17, 24, 31, 1919, Jan. 7, 1920. 

2 Herzberg: Papierprufung, Berlin, 1907. 

386 



ESTIMATION OF FIBRE CONTENT 387 

in a sample of paper and it is therefore the universal method 
for making a fibre analysis. The method is rapid, and in the 
hands of an expert is fairly accurate, but it is probably not 
desirable to attempt to estimate percentages much closer than 
5 per cent. The accuracy attainable depends upon two factors 
(1) the kind of mixture under examination, i.e., whether two or 
more fibres, and how beaten and (2) the experience and care of 
the observer. As a rule, the opinion of one thoroughly trained 
and careful analyst is more exact than the average judgment of 
several inexpert men who have spent collectively much more 
time on the examination. 

The microscope used should be of some standard make so that 
attachments may be added from time to time as seems desir- 
able. The particular kind of microscope and whether monocu- 
lar or binocular is largely a matter of personal preference. This 
also holds true of the magnification employed, some advocating 
45 diameters and others 120 or even as high as 160 diameters. 
An instrument with two-thirds and one-sixth inch objectives 
and 1- and 2-inch eyepieces will be found to give as great a 
range of magnification as is necessary for all ordinary paper- 
mill work. A substage condenser and iris diaphragm should 
by all means be included and it is very desirable to add a stage 
micrometer and an eyepiece micrometer. 

Estimation of Fibre Content. In order that the sample taken 
shall be representative several small pieces should be clipped 
from various parts of the sheet, or if several sheets are available 
small pieces should be taken from each. These should be placed 
in a dish, small flask, or any suitable container, covered with 
0.5 per cent caustic soda solution, and heated to the boiling 
point in order to dissolve sizing or binding materials. The 
samples are then washed several times in water, rolled into a 
ball and kneaded between the thumb and finger and then re- 
duced to a pulp by shaking vigorously in a test tube about 
half full of water. A small sample is then removed from the 
test tube by means of a needle, placed on a microscope slide 
and the water removed by touching the drop with a piece of 



388 PAPER TESTING 

folded filter paper of ordinary quality. The fibres are covered 
with a drop or two of Herzberg's stain, carefully separated by 
the aid of microscope needles, so that they will not lie too much 
in a bunch, and they are then covered with a cover glass. The 
slide is then ready for examination by means of the microscope. 

In preparing the sample for examination a number of pre- 
cautions must be observed if good results are to be obtained, 
and a discussion of some of these important points will be help- 
ful, at least to those who are just beginning the work. 

There are several methods of removing a representative 
sample from the test tube. Spence and Krauss l prepare a 
rather dilute pulp in a test tube about f X 8 ins. and for re- 
moving the sample use a glass tube 10 ins. long by -jVin. in 
diameter. This tube is fitted with a small rubber bulb at one 
end while the walls at the other are rounded to present a smooth 
surface. The test tube is well shaken, the dropper quickly 
inserted 2 ins. below the surface, two bubbles of air expelled 
and about half an inch of mixture drawn into the tube. This 
entire portion is transferred to slides, making four drops in all, 
and the water removed by evaporation in an air bath. The 
slides are then ready to stain and examine. 

Another and more usual method is to prepare the mixture in 
a smaller test tube, say f X 6 ins., and after shaking vigorously 
remove the sample by inserting a microscope needle and taking 
out a small bunch of the fibres. This method is better for 
long-fibred stock such as bond, ledger and writing papers, while 
the first method is safer for ground-wood papers and others 
where very short fibres are present. 

A modified form of the second method, which makes it appli- 
cable to all grades of paper, is to prepare the mixture of such 
density that on shaking the test tube and then placing it up- 
right, small clots of fibre will remain adhering to the walls of 
the tube above the liquid. The sample is then obtained by 
removing all the fibre included in one of these small clots. 

Removal of water from the sample before staining may be 

1 Spence and Krauss: Paper, 20, 1917, p. 12, May 23. 



ESTIMATION OF FIBRE CONTENT 389 

done with filter paper or by drying as already outlined, or a 
blotting paper of firm texture may be pressed down directly 
on the drop on the slide. This removes the water and leaves 
the fibre adhering to the slide ready for staining. If a firm 
blotter, free from lint, is used and any loose fibres are removed 
by blowing upon its surface just before applying it, no contami- 
nation of the sample need be feared. Another method is to place 
the sample removed by the needle from the test tube directly 
upon a piece of suitable filter or absorbent paper; this takes up 
the water and the fibre can then be transferred to the slide. 

The use of very thin cover glasses for covering the stained 
specimen is only to be recommended when very high magnifi- 
cation is to be used. In nearly all fibre analysis it is quite 
sufficient to use a second thin microscope slide as a cover. This 
permits several fields to be prepared on one slide and eliminates 
much breakage. The slide as a cover glass also possesses an- 
other advantage over the lighter and thinner form: if the sample 
is well loosened up with the needle so that no lumps remain 
and the slide is then dropped onto it from a distance of half an 
inch or so a very even distribution of the fibres can be obtained. 

The Herzberg stain, which is very generally used, is made up 
according to the following formula: 

Solution A. 20 grams zinc chloride dissolved in 10 c.c. of 
distilled water. 

Solution B. 2.1 grams potassium iodide and 0.1 gram iodine 
dissolved in 5 c.c. of distilled water. 

Prepare the two solutions separately, mix and allow the mix- 
ture to stand several hours or until all sediment has settled out. 
The clear liquid is then decanted and is ready for use in staining 
fibres; it should be kept in a brown glass bottle or else in the 
dark. This stain gives different colors with different kinds of 
fibres; ground wood, jute, flax tow, uncooked manila hemp and 
practically all highly lignified tissues are colored yellow or lemon 
yellow. Thoroughly cooked and bleached soda and sulphite 
pulps as well as bleached straw and esparto fibres are colored 



390 PAPER TESTING 

blue or navy blue. Cotton and linen rags, thoroughly cooked 
and bleached manila hemp and some of the Japanese fibres are 
colored wine red. 

It is very essential that this stain be so made up as to give 
satisfactory colors on the different fibres. Its quality should 
be proved by staining a mixture of fibres known to contain 
about equal proportions of rag, bleached sulphite and bleached 
soda fibres. If the stain is satisfactory, the soda pulp should 
stain a dark blue color, while the sulphite, because of its thinner 
walls, will be a light blue, and the rag fibres will be red or wine- 
red. If the blue is not clear but tends toward the violet, too 
much iodine is present and more water or zinc chloride should 
be added. A stain which gives the best results with ground 
wood will not always be entirely satisfactory with mixtures of 
well-bleached fibres and if widely varying papers are to be 
examined, it is well to keep on hand a number of stains so ad- 
justed that one suitable for any grade of fibre is available. One 
should be prepared to give a bright lemon yellow on ground 
wood; a second should give the colors already mentioned on 
sulphite, soda and rag fibres, etc^ 

A stain which is considered by some to be better than the 
Herzberg stain is made up as follows: 

Solution A. 1.3 grams iodine and 1.8 grams potassium iodide 
in 100 c.c. of water. 

Solution B. A clear, practically saturated solution of calcium 
chloride. 

In using this stain apply a drop or two of solution A to the 
moist fibres on the microscope slide. After a minute or so re- 
move the stain by means of a blotter and immediately put on 
a drop or two of solution B. Pull the fibres apart and distrib- 
ute them by means of needles as before and drop on a cover 
glass or thin microscope slide. Any excess of solution B should 
be removed by absorbing it with moist blotting paper. This 
stain is also selective in its action, the colors produced being as 
follows : 



ESTIMATION OF FIBRE CONTENT 391 

Red or brownish red: Cotton, linen, hemp, ramie. 

Dark blue: Bleached soda pulps from deciduous woods. 

Bluish or reddish violet: Bleached sulphite fibres and the 
thoroughly cooked part of the unbleached sulphite. 

Greenish: Jute, manila and the more lignified fibres in un- 
bleached sulphite. 

Yellow : Ground wood. 

As with the Herzberg stain this one should be adjusted by trial 
on known mixtures of fibre until it shows satisfactory differ- 
ences in color. The two solutions should be protected against 
evaporation and dust but light does not change their staining 
properties to any extent. 

In estimating the fibre content of a paper no account is taken 
of the size, clay, alum, etc., which may be present; the paper is 
therefore considered as being all fibre and the sum of the per- 
centages of the various kinds is made to equal 100 per cent. 
The estimation should be based on the examination of at least 
two samples of fibre removed from the test tube and in some 
cases where especial accuracy is desired it is well to examine four 
separate slides. A set of standard samples containing known 
percentages of the different ingredients is very useful in making 
comparisons with unknown samples and should be used occa- 
sionally to refresh the judgment of the analyst. 

There are two methods of determining the percentage of the 
various fibres, one is the "count method," while the other is 
known as the "estimation method." In the first method the 
fibres of each kind are counted and from the figures obtained 
the percentage of each is calculated. The estimation method 
depends upon the comparison of the unknown sample with 
standard mixtures of known composition. The accuracy of 
this method depends upon the experience of the analyst and 
upon continual reference to the known standards. It is prob- 
ably fully as accurate as the count method, is considerably 
quicker, and is much easier to teach to a beginner. For these 
reasons it is usually preferred to the count method. In using 



392 



PAPER TESTING 



either method it is quite obvious that the analyst must be thor- 
oughly familiar with the size, shape, and markings of the various 
fibres and with the appearance of any ducts, cells, or foreign 
matter which habitually accompany them. Without such knowl- 
edge it is useless to attempt to make a fibre analysis. 

A third method has recently been proposed by Spence and 
Krauss 1 to enable an estimation to be made of the different 
kinds of fibres in a mixture containing such fibres as hemlock, 
beech, poplar, birch, maple, etc. Four samples are made up 
by the method of Spence and Krauss already given. Each 
slide is examined under the microscope and the lengths of the 
various fibres are measured in terms of the diameter of the 
observed field. The magnification recommended is 160 diam- 
eters and an adjustable stage is essential in order to cover sys- 
tematically the entire sample on each slide. After all four 
samples have been examined the figures are added together to 
get the total length of each kind of fibre present. This total 
length multiplied by a weight factor, which varies with different 
kinds of wood, gives a set of directly comparable results which 
may be converted into the per cent of each kind of fibre present. 
The weight factors given are as follows: rag pulp i; hemlock 
pulp 0.870; poplar pulp 0.454; birch pulp 0.652; beech pulp 
0.525; maple pulp 0.365. Where a mixture of fibres from 
deciduous woods is under examination the number of counts of 
each kind to which the weight factor is to be applied may be 
determined from an examination of the number of ducts present. 
It was found that the proportion of ducts and fibres in different 
woods was as follows : 




1 Spence and Krauss: Paper 20, 19 17, May 23, p. n. 



UNBLEACHED SULPHITE DETERMINATION 393 

This method is too slow to be used where many routine 
analyses are to be made daily but its accuracy recommends it 
particularly for settling cases of dispute between different 
authorities. 

Unbleached Sulphite Determination. The method given is 
that worked out by Bright. 1 

"The principle of the method is first to stain the fibres with 
Cross and Bevan's ferric ferricyanide solution, which colors the 
unbleached sulphite green, on account of the lignin contained 
in it, and leaves the bleached sulphite colorless. This alone 
gives a good distinction, but by subsequently staining with a 
red substantive dyestuff , the green of the unbleached is changed 
to a very pure blue, the bleached being colored red, thus giving 
a most striking contrast. 

"The problem is to adjust the treatment with the two solu- 
tions to bring out the sharpest contrast. If the treatment with 
red is too severe, some of the unbleached fibres are likely to be 
colored purplish, or in extreme cases take on a dull, dirty red 
color. On the other hand, if the treatment with ferric ferricy- 
anide is continued for too long a time or at too high a tempera- 
ture, the reagent has a tendency to decompose and form a 
deposit on the slide as well as on the bleached sulphite, so that 
the latter turns a dull purplish color when subsequently stained 
with red. 

"The results depend on three factors — namely: (1) the con- 
centration of the solution, (2) the temperature at which each 
is applied, and (3) the length of time each is allowed to act. 

" The solutions are prepared according to the following pro- 
cedure: 

Ferric Ferricyanide 

Sol. A. — N/ioFeCl3 — 2.7 grams FeCl3 6H2O per 100 c.c. 
Sol. B. — N/10 K 3 Fe (CN)6 — 3.29 grams per 100 c.c. 

" After diluting to the mark with distilled water, filter through 
dry filters into clean, glass-stoppered bottles — protect from 
dust. 

1 Bright: Paper 20, 1917, Aug. 29, p. 11. 



394 PAPER TESTING 

" Equal volumes are mixed fresh whenever the reagent is used. 

Substantive Red 

Benzopurpurin 4B extra (Bayer Co.) gm. 0.4 

Oxamine brilliant red BX (Badische Co.) gm. o. 1 

Distilled Water c.c. 100 

" Have the water hot and stir in the dyes slowly. 

" The stain is placed in a tall, narrow, cylindrical beaker, which 
is set into a water bath. The slides are suspended in the beaker 
by a clamp which holds them at their upper ends, the clamps 
resting across the top of the beaker. A thermometer is sus- 
pended in the beaker of stain beside the slides. The beaker 
should be as small as possible so as not to use up too much 
stain at one time. 

" Staining with ferric ferricyanide is done as follows: 

" Mix equal volumes of two fresh solutions and heat to 35° C. 
regulating the waterbath so that it will remain within 1 deg. of 
the temperature named, for 15 minutes. The dry slide is then 
dipped in water to moisten it uniformly, so that air bubbles 
will not be formed when it is immersed in the stain. If air 
bubbles are formed the fibres under the bubbles will not be 
stained. If dipping in water still leaves bubbles, they can be 
removed by blowing across the slide from the edge. The slide 
is then suspended in the stain and left there for 15 minutes at 
35 C. It is then removed and washed by dipping in and out 
of a beaker of distilled water six times and repeating the proc- 
ess in a fresh beaker of water. The slide can then be placed 
wet into the red solution, but it is perhaps best to dry it out 
so that the fibres will be stuck on tightly again in case they have 
been loosened to any extent by the treatment. 

" Staining with the substantive red solution is done as fol- 
lows: 

" A fresh solution is heated to 45 C, and the slide, after mois- 
tening and excluding bubbles as before, is suspended in the solu- 
tion for five minutes at 45 C. and immediately washed in two 
beakers of distilled water. 



• 



MACHINE DIRECTION 395 

"The slide is then dried and a cover glass placed on with a 
drop of balsam. 

" To get the clearest, brightest results, distilled water must be 
used throughout, and the staining solution must be fresh. The 
two solutions for ferric ferricyanide will keep well if placed in 
separate bottles. Equal volumes are mixed together immedi- 
ately before using. The red solution should be made freshly 
each time for the best results, as it gets thick and stringy on 
standing, especially when it is being heated up continually. 

" This method of staining will in general give a distinction be- 
tween pure cellulose fibres and those which contain lignin. 
Rags, bleached sulphite, soda pulp or any thoroughly bleached 
materials are stained red, while unbleached sulphite, ground 
wood, jute, or any lignified materials are stained blue." 

Physical Tests 

Machine Direction. Several methods are available for de- 
termining the machine direction in a sample of paper. It may 
sometimes be ascertained by mere inspection of the sheet, as 
the formation noted on looking through it is often conclusive 
to the trained observer. 

The usual machine wire imparts to the sheet of paper a "wire 
mark" consisting of a series of diamond-shaped marks, the long 
diagonal of which points in the machine direction. If the wire 
mark is sufficiently prominent so that its direction can be 
determined this will establish the machine direction. 

If the paper is well sized and a circular piece is cut out and 
moistened on one side by floating on water, it will tend to roll 
up into a cylinder whose axis is in the machine direction of the 
sheet. If the paper is unsized it will become entirely soaked 
through on floating on water and will not curl up. This may 
be avoided by sizing the paper with an alcoholic solution of 
rosin, or with a solution of gelatine in water, drying and then 
making the test. 

Another method of determining the machine direction is to 
cut two narrow strips of the paper, one from either direction, 



396 



PAPER TESTING 



place these one over the other and hold them upright in the 
fingers. They will droop over of their own weight and if they 
cling close together the under strip is in the machine direction 
while if the under strip falls away from the upper the latter is in 
the machine direction. 

The form of the break made by the Mullen tester shows the 
machine direction, as the longest, or chief, line of rupture is 
always across the sheet. This is shown in Fig. 43, which illus- 







Fig. 43. Lines of Rupture in Mullen Test 

trates four typical ruptures and in which the arrows indicate the 
machine direction. 

Wire or Felt Side. In many cases this may be determined 
very easily by a simple inspection but in some papers the wire 
marks do not stand out at all plainly. Sometimes they may be 
made more prominent by plunging the sample for a moment 
into water and draining or blotting off the excess. The moist- 
ure causes the fibres to expand, thus undoing the work of the 
calenders and restoring the texture of the sheet as it left the 
machine wire. Inspection of a sheet thus dampened will often 



WEIGHT OF SAMPLE 397 

show that the wire marks stand out plainly, where before they 
were indistinguishable. This method very often proves satis- 
factory even for coated papers. 

Weight of Sample. The weight of a sample of paper is usu- 
ally expressed as so many pounds per ream of a given size, but 
the number of sheets per ream and the standard size of the sheet 
are more or less variable in the different branches of the in- 



1 



V 



«W> ■-■-•-'" 



P: 




Fig. 44. Beam Type of Paper Scale 

dustry. Where a full sheet of paper is available the weight 
per ream may be conveniently found on scales of the type 
shown in Fig. 44. The folded sheet is placed on the hooks 
and the weight per ream is shown by the position of the sliding 
poise on the beam. This instrument, which is largely used for 
mill work, is usually graduated for reams of both 480 and 500 
sheets. 

Two representative scales of the quadrant type are shown in 
Fig. 45 and Fig. 46. With these the weight per ream in pounds 





^•~^^~-~ 


' : GBBfl3ffl ' 


■ 1 \ 


V-0m 


^^^WF X /-/ 


■ ^^: 










M^fe> 




^^sjH^K^^^^^SjT - 








C ^-< •--. 


*©* • ■ '• JO 






W^- 




,;..i 



Fig. 45. " Quick-stop " Paper Scale 
Courtesy of B. F. Perkins &° Son, Inc. 




(398) 



Fig. 46. Basis-weight Scale 
Courtesy of Thwing Instrument Company 



THICKNESS 



399 



per 500 sheets is read off directly on the scale and no movement 
of weights is necessary. 

In the case of very small samples a piece of known area 
should be weighed on a chemical balance and the ream weight 
calculated by the following formula: 

(Wt. in grams) X (1-103) X (area of trade size desired) 
Area of sample in square inches 
= Weight on trade size desired. 

Thickness. The thickness of a paper may best be deter- 
mined by means of a spring micrometer having a hand that 




Fig. 47. Thickness Gauge 
Courtesy of B. F. Perkins & Son, Inc. 

travels around a circular dial which is graduated in thousandths 
of an inch. One of the many such instruments is shown in 



400 PAPER TESTING 

Fig. 47. This type of tester should not be read closer than half 
a thousandth as this is about their limit of accuracy. 

Thickness may also be measured by means of an ordinary 
micrometer caliper but the amount of pressure is not easily con- 
trolled unless it is supplied with a ratchet device which prevents 
an excessive pressure being applied. This is not so accurate as 
the spring type but is useful for approximate work around the 
mill. 

It is advisable to have all thickness gauges tested before use. 
This may be done by securing a set of standard sheet-metal 
leaf gauges which range from 0.001 to 0.015 in. These should 
be used occasionally to make sure that the instrument for 
measuring thickness remains accurate. 

It has been suggested by the Committee on Paper Testing 
that the relative compactness of papers be calculated as follows 
for purposes of comparison. 

Thickness in thousandths of an inch X 10,000 
Weight 25 X 40,500 
= Relative compactness. 

Bulk. The " bulk " of a paper is the thickness of a certain 
number of pages and is a factor which must be taken into con- 
sideration in planning a book which must not exceed a definite 
thickness. It is usually measured by making up a "dummy" 
or cutting out short strips, piling them up to the required num- 
ber and measuring its thickness with the ordinary graduated 
sliding clamp. In using this the pressure used must be speci- 
fied as heavy, medium, or light and this introduces an element 
of uncertainty into the results. 

The so-called "pressure bulker," Fig. 48, made by B. F. 
Perkins and Son has been made to eliminate these troubles. 
In this instrument the "dummy" is put under a definite pres- 
sure which is read in pounds per square inch on the dial and 
the thickness in inches is read on a scale at the side. 

Opacity. The opacity or translucency of a paper may be 
measured by the "Contrast ratio" method using a Martens 



OPACITY 



401 



photometer in a specially constructed box. 1 This method in- 
volves a determination of the difference in photometric bright- 
ness, or contrast, between a black and white spot when covered 
with the material to be tested. 




Fig. 48. Pressure Bulker 

Provided this apparatus is not available, good comparative 
tests can be made by cutting a small, sharp-edged opening in a 
piece of cardboard and placing this over a source of intense 
light. Pieces of the paper are then laid over the opening one 

1 Bureau of Standards Circular No. 63. 



402 



PAPER TESTING 



at a time^ and the number of sheets required to completely 
obliterate the light is noted. By determining the thickness per 
sheet the absolute thickness of the paper required to obliterate 
the light can be calculated. 

Gloss or Glaze. An instrument to measure the gloss or 
glaze of paper has been devised by L. R. Ingersoll. 1 It was 
found that light specularly reflected from paper at an angle of 
57.5 degs. was almost completely plane-polarized and working 
on this basis the instrument was designed to measure the gloss 




Fig. 49. Ingersoll Glarimeter 

by determining the fraction of the light reflected from the paper 
at an angle of 57.5 degs. which is polarized. In using the in- 
strument, light from a tungsten lamp is reflected from the 
paper through a diaphragm, part of the opening of which is 
covered with a small Nicol prism and the rest with a piece of 
smoked glass which absorbs about one-half the light. The 
beam then passes through the eyepiece which is another Nicol 
prism mounted to rotate in a divided circle which reads with 
the aid of the vernier to five minutes of arc. On looking into 
the eyepiece a divided field is seen and a measurement is made 

1 L. R. Ingersoll: Electrical World, 63, 1914, 645. 



TENSILE STRENGTH 403 

by turning the divided circle until the dividing line between the 
two parts of the field disappears. From the average of a num- 
ber of such measurements the percentage gloss may be found 
by consulting a table which accompanies the instrument. 

Fig. 49 gives a perspective view of the Ingersoll glarimeter. 

In using this instrument it must be remembered that the 
results are comparable only when papers of the same color are 
considered, since a black paper having the same glossy surface 
as a white paper would reflect an entirely different per cent of 
light, due to the absorption of the black color. Since the great 
majority of papers examined are white, this limitation is not a 
serious objection. 

Tensile Strength. The tensile strength of a paper is deter- 
mined by the load, in pounds, required to break a strip of it. 
The tensile strength machine best known in the paper industry 
is the Schopper tensile machine, illustrated in Fig. 50. 

In this device a strip of paper 15 mm. (approximately H in.) 
wide by 180 mm. long (approximately 7 T \ ins.), is clamped at 
each end and the clamps are moved apart until the strip is 
broken. A suitable device indicates the pull in kilograms (ap- 
proximately 2.2 lbs.) required to break the strip. It is recom- 
mended that the load in kilograms per 15 mm. width strip, be 
converted into pounds per inch of width by the following 
formula : 

(3.73) X (Tensile strength in kg. per 15 mm. width) 
= Tensile strength in lbs. per 1 in. width. 

A tensile strength factor may be determined by the following 

formula : 

( Tensile strength in lbs, per 1 in. width X 
Weight 25 X 40,500 / 

= Tensile strength factor. 

The usual factor for tensile strength is known as the breaking 
length. This is the length of a strip which, if suspended at 
one end, would break of its own weight. The following formula 
may be used to determine the breaking length of a sample: 



4°4 



PAPER TESTING 

(Tensile strength per i in. width) X (13,889) 
(Weight of a sheet 25 X 40,500) 
= Breaking length in yards. 




Fig. 50. Schoppee. Tensile Machine 

Stretch. The amount of elongation at the instant of rupture 
of a strip of paper under tension is measured on the S chopper 
tensile strength machine. The result is figured as a per cent of 
the total, original length. 

Bursting Strength. There are two general types of apparatus 
used to determine bursting strength. One is of the hydraulic 



TENSILE STRENGTH 



40S 




Fig. 51. Mullen Tester 




Fig. 52 . District or Columbia Paper Tester 



406 



PAPER TESTING 



type, in which the paper is clamped against a rubber diaphragm, 
through which the pressure is applied to a circular area of the 
paper measuring one square inch. The Mullen tester, Fig. 51, 
and the District of Columbia paper tester, Fig. 52, are of the 
hydraulic type. The second type of bursting strength apparatus 
is of the spring operated metal plunger design, in which the 
paper is clamped between annular rings, through which a spring 
operated plunger is forced. The Ashcroft tester, Fig. 53, is the 
only one of the above type now on the market. 




Fig. 53. Ashcroft Tester 

The bursting strength to be of greatest use must be expressed 
in terms of the weight of the sample. This ratio of strength 
to weight may then be directly compared with the strength ratio 
of any other paper, if the same standard size sheet is used in 
each case. The strength ratio is expressed as a percentage. 

Bursting strength X 100 



Strength ratio = TTT . . 

Weight m pounds (on a size 25 X 40,500) 

Folding Endurance. The folding endurance of a paper is 
measured by a machine in which a strip of paper is caused to 



FOLDING ENDURANCE 



407 



fold back and forth upon itself until it is worn through. The 
Schopper Folding Machine, which is the only device so far 





Fig. 54. Schopper Folding Machine 

made to carry out this test, is shown diagrammatically in front 
view, and from above in Fig. 54. 

In making a test the slot cut in the thin metallic plate fastened 



408 PAPER TESTING 

to the end of the shaft (13), is brought exactly in line with the 
jaws (7) and a strip of paper cut accurately, 15 mm. in width 
and 100 mm. in length, is firmly clamped between the jaws and 
through the slot. The paper is then put under tension by pull- 
ing out the shafts (4) to which the jaws are fastened by an 
intermediate spring (3). The shaft (13) is given a reciprocat- 
ing motion by the revolution of the wheel (19), and the paper 
is folded and refolded over the edges of the slot in the thin 
metallic plate and around the rollers (12), the revolving of 
which eliminates friction between the paper and the rollers. 
Twice in each revolution of the drive wheel (19), the jaws are 
pulled out to what may be termed the maximum position and 
the paper is then under a tension of 1000 grams. When the 
slot in the metallic plate is in line with the jaws the test strip 
is under the minimum tension of approximately 730 grams. 
Most papers stretch slightly under these tensions, which are 
thereby reduced more or less, with the result that a somewhat 
higher folding number is obtained. The paper is weakened in 
the crease made by the repeated folding and finally broken by 
the tension. The number of double folds is automatically 
recorded on the dial (18). 

The folding strength of paper is dependent not only upon the 
strength and durability of the paper, but also is very largely 
influenced by the relative humidity. To perform this test in 
the most accurate manner it is therefore necessary to keep the 
relative humidity constant for all tests. This can only be done 
by the use of a room where the humidity is under control. 
Where such a room is not available then note must be made of 
the per cent relative humidity of the air at the time of the test. 
No tests should be attempted when the humidity is either very 
high or very low. A relative humidity between 65 and 70 
per cent is most easily attained throughout the year and is the 
standard humidity recommended. 

The folding factor is determined by the following formula: 

Folding endurance t- 1 t r ^ 

,„ T . , & r = Folding factor. 

(Weight 25 X 40,500) 



TEARING TEST 409 

The folding factor will vary between about 0.1 and 200. 

The standardization of the folding tester and the accuracy of 
the results obtained have been very carefully investigated by 
Veitch, Sammet and Reed 1 who consider it valuable for indi- 
cating the probable durability of paper and its suitability for 
specified purposes. 

Tearing Test. This method of testing paper is not yet stand- 
ardized though much interest has recently been shown along 
this line and several methods have been proposed for determining 
the tearing strength of paper. 

Case 2 cuts a strip z\ ins. by 1 in. which is slit lengthwise for a 
distance of 2J ins., leaving a distance of \ in. to be torn. The 
strip on one side of the slit is fastened in a clamp and to the 
other strip is suspended a small bucket into which water is 
allowed to flow until the two strips are torn apart. The weight 
of the bucket and water in grams is taken as the tearing resist- 
ance number. 

The S chopper tensile machine was used by Wells 3 who removed 
the weight from the arm and used only the arm and the milled 
screw with the pawls held out of action. To eliminate the local 
variation in a single sheet, several samples from the same sheet 
were torn at once, half being cut across and half with the grain. 
A speed of tearing of i| ins. per minute was used and readings 
taken every five seconds while making a tear of 3 ins. This 
method was found to give good check results provided the speed 
of tearing was constant. 

A tearing tester recently devised by Thwing is shown in Fig. 
55. A small sample of paper is cut and punched by a special die 
and attached to two pins one of which is attached to a movable 
weight on an arm carrying a recording pen while the other is 
attached to a motor driven, sliding record card holder. This 
holder is caused to move away from the pin on the weight arm, 
thus tearing the paper along the line of perforations. The record 

1 Veitch, Sammet and Reed: Paper, 20, 1917, May 30, p. 13. 

2 Case: J. Ind. Eng. Chem., 11, 1919, 49. 
s Wells: Paper, 23, 750, Feb. 12, 19 19. 



4io 



PAPER TESTING 



shows graphically the force in grams required to tear the paper 
between each two perforations, thus giving five peaks, the 
average of which is taken as the tearing strength. 




Fig. 55. Thwing Tearing Tester 
Courtesy of Thwing Instrument Company 

Absorbency. The absorbent power of a paper is generally 
measured by suspending strips vertically with their lower ends 
dipping into water and noting the height to which the water 
rises in ten minutes. The average for several strips cut in both 
directions should be taken as the figure for absorption. 

This method is criticized by Reed l because it employs water 
instead of ink but still more because it is unaffected by the bulk 
or weight of the paper. He proposes allowing 1 c.c. of a standard 
ink to fall from a pipette upon the surface of a 4-in. square of the 
blotting paper which is placed over a tumbler or beaker of 

1 Reed: J. Ind. Eng. Chem., 10, 1918, 44. 



PERMEABILITY TO AIR 411 

such size that the edge of the spot will not touch the glass. The 
time for the complete absorption of the ink is recorded. In this 
test attention must be paid to the temperature of the ink, the 
delivery time of the pipette, the distance of the tip above the 
surface of the paper, and the amount of liquid used. All of 
these factors must be standardized if comparable results are to 
be obtained. 

Volumetric Composition. The determination of the volume 
composition of a paper is at best only an approximation but it is 
at times desirable to carry it out. The weight of a cubic centi- 
meter of the paper is first ascertained by calculation from the 
thickness of the sample and the weight of a measured area. The 
percentage by weight of the various materials present, fibres, clay, 
size, etc., is then determined in the usual way and from this the 
weight of each in a cubic centimeter of the paper is calculated. 
The weight of each substance in grams divided by its specific 
gravity gives the volume occupied by it, and the sum of all of 
these volumes subtracted from 1.0 gives the volume of air per 
cubic centimeter of paper. This method is fairly accurate 
when only fibres, clay and rosin are present but when other sub- 
stances are added, as in coated papers, the problem becomes more 
complex and the results less reliable. 

If the volume of air per cubic centimeter of paper is the only 
information needed it may be obtained by determining the actual 
specific gravity by weighing in air and then in oil of known dens- 
ity exactly as in making specific gravity determinations in water. 
It will be found necessary to expose the paper, submerged in 
oil, to reduced pressure for some time in order to be sure that 
all air is removed and replaced by oil. 

Permeability to Air. No simple and accurate apparatus for 
measuring this property of paper is available. Herzberg * has 
made measurements by passing air through a definite area of 
the paper under standardized conditions and measuring the 
amount passed by a gas meter provided with a special overflow 
to equalize the level on the two sides of the meter. This method 

1 Herzberg: Mitt. k. Materialpruf, 1915, 33, 142-144. 



412 PAPER TESTING 

doubtless gives reliable comparative tests but the apparatus is 
not of a kind which is generally available. 

In the case of waxed or waterproofed papers it has been pro- 
posed by Seiter x to use the paper as a diaphragm in a dialyzing 
apparatus, placing ferric chloride above the paper and potassium 
ferrocyanide below. The time required for the development of 
Prussian blue is a measure of the porosity of the paper. 

Grease-Proof Properties. The surest method of determining 
whether a paper is grease-proof is to place the sample on a piece 
of white paper, pour on it a small quantity of oil of turpentine 
and rub it around with a bit of absorbent cotton. If the white 
paper becomes stained with the oil the sample is not grease- 
proof. 

A rough test for parchment papers is to heat the sample mo- 
mentarily over a flame and note the formation of blisters. Pin 
holes will prevent the formation of blisters while on the other 
hand the more impervious the surface the more blisters will be 
formed. This test is not absolutely reliable, as some papers which 
blister are not grease-proof, while some which do not blister are 
satisfactory in this respect; it is, however, reliable in the ma- 
jority of cases. 

Degree of Sizing. For book and magazine papers which are 
ordinarily not sized very hard a sufiiciently accurate test may 
be made by floating a small piece of the paper on a bath of 
ink and noting the time required for the ink to penetrate to the 
upper surface. In this test a standard ink should be used and it 
should be thrown away when used once and not returned to the 
bottle. The temperature of the ink has a very great influence 
on the time of penetration and it should be maintained within 
half a degree throughout the tests. The personal factor of course 
plays a very important part in this test and to make results 
strictly comparable they should all be obtained by the same per- 
son. 

Attempts have been made to eliminate the personal equation 
by measuring the conductivity of the paper as it is gradually 

1 Seiter: Chemist-Analyst No. 21, April, 19 17. 



DEGREE OF SIZING 413 

penetrated by an electrolyte. Okell 1 applies the solution of 
the electrolyte to both sides of the paper in a specially con- 
structed cell which permits of slight but constant pressure on 
both sides of the sheet. A slightly modified form of this cell has 
also been employed by Clark and Durgin. 2 The results obtained 
are interesting and warrant its use for scientific investigations 
but the apparatus does not appear well adapted to the rapid 
work required where a large number of routine tests must be 
made in the shortest possible time. 

For high grade papers, such as surface sized writing papers, 
the notation test does not indicate sufficiently well the quality 
of the sizing. For such papers the method proposed by Sammet 3 
should be used. 

This method involves the drawing of a strip of paper over the 
surface of an iron tannate ink and allowing it to drain and dry 
naturally. Upon examination of the surface with a low power 
microscope, a well sized paper will show no indication of the 
fibre having absorbed the ink. Any variation in the depth of 
color on the surface will indicate a lack of uniform sizing. This 
test may be still further developed by erasing the surface with 
an ink eraser (a spun glass eraser is most suitable) and again 
dipping the sheet as before. A paper well sized throughout the 
sheet will show little or no additional absorption of ink at the 
erased spot. This test is only comparative but may be valuable 
to a mill in checking the daily progress. 

The ink used for the above test is made as follows: 

Tannic acid (dry) 23.4 grams 

Gallic acid (crystals) 7 7 grams 

Ferrous sulphate 30 grams 

Dilute hydrochloric acid (U. S. P.) 2 <. o c.c. 

Pheno1 1 . o gram 

Blue Dye (Bavarian Blue S. & J. No. 478) 2.2 grams 

Water to make up to 1000 c.c; allow to settle, and decant from any sediment. 

Note. — Any water-soluble aniline blue, as methylene blue, may be used in 
place of Bavarian blue. 

1 Okell: Paper, April n, 1917, 20. 

2 Clark and Durgin: Paper, 22, 1918, 223. 

3 Sammet: Bureau of Chem. Circular No. 107, also Paper, 10,1913, No. 9, p. 15. 



4 I4 PAPER TESTING 



Chemical Tests 



Moisture in Paper. In most cases the moisture may be de- 
termined easily and accurately by weighing a sample into a 
weighing bottle with a ground-glass stopper, drying at ioo° to 
105 C, closing the bottle, cooling in a desiccator and again 
weighing. The loss in weight represents moisture. In no case 
where the work demands any degree of accuracy should the 
weighing of the dried paper be done in the open air because the 
dry paper absorbs moisture very rapidly from the surrounding 
atmosphere. 

This procedure is inaccurate in some cases where substances are 
present which lose water of crystallization, or of constitution, at 
the temperature named. This is particularly true of papers where 
calcium sulphate is used as a filler or where satin white is used in 
the coating. In these cases drying at ioo° to 105 C. expels three- 
fourths of the water of crystallization of the calcium sulphate 
and this loss gives an entirely fictitious value to the hygroscopic 
moisture. In such cases the only expedient seems to be to dry 
the samples to constant weight in a desiccator over sulphuric 
acid. 

Ash Determination. A sample of one gram of the paper is 
ignited in a weighed dish, over a burner, or in a muffle, until all 
carbon is burned off. The dish is then cooled in a desiccator 
and weighed; the increase in weight represents ash and by mov- 
ing the decimal point two places to the right it may be expressed 
at once as percentage of the paper taken. 

If the ash is to be cooled and weighed in the dish the ignition 
may be made in porcelain, platinum or any material not changed 
in weight by heating to a bright red heat, but platinum will be 
found to be the cheapest in the long run because it cools quickly, 
is practically constant in weight and above all because the 
ignition is more rapid than in porcelain or silica. Because of the 
greater speed of combustion a shallow dish is much preferable 
to a crucible and a still further gain may be made by covering 
the dish with a curved piece of platinum foil which reflects the 



ASH DETERMINATION 415 

heat downward but allows the entrance of plenty of air. With 
four such dishes it is easily possible to weigh out twelve samples, 
ignite, cool, weigh and record the results within an hour. 

The sample of paper need not be weighed closer than 0.005 
gram except in cases where extreme accuracy is desired and then 
the sample should be weighed in the bone dry condition in a 
weighing bottle. Meker burners have been found very satisfac- 
tory for ash determinations, being considerably more rapid than 
the ordinary Bunsen. During burning care must be taken that 
no ash is blown out of the dish by strong air currents as this is 
likely to take place especially with the light, fluffy ashes from 
unloaded or lightly loaded papers. This same danger must be 
guarded against when removing the covers from the desiccators 
in which the dishes are cooled. The use of desiccators may be 
avoided and some time saved by pouring the ignited ash into a 
counterpoised aluminum pan as soon as the dish is cool enough to 
avoid danger of loss from convection currents. The ash will cool 
almost instantly and may be weighed at once. 

The ash as finally obtained includes all non- volatile and incom- 
bustible matter in the paper. It may come from at least five 
sources: 1, materials in the pulps employed; 2, the loading or 
filling materials used; 3, substances used in coating or surface 
sizing; 4, mineral coloring matters or pigments; and 5, ash due to 
alum and size. It is possible that a paper may have an ash 
content as high as 5 per cent without being loaded but if this 
figure is exceeded it is safe to say some filler has been employed. 
In this connection it is interesting to note the following percen- 
tages of ash in fibrous raw materials as given by Wrede. 1 

Stock Percentage ash 

Bleached linen half stuff o. 1 2-1 .'86 

Bleached cotton half stuff o. 24-0. 79 

Unbleached cotton half stuff o. 24-1. 12 

Sulphite, unbleached o. 48-1 . 25 

Soda o. 36-1.40 

Adansonia . . .- 5. 70-7. 19 

Japanese fibres 2.5 

1 Wrede: Paper, Jan. 31, 191 2. 



41 6 PAPER TESTING 

In coated papers the ash, of course, includes that from the coat- 
ing as well as from the body stock. If it is desired to examine each 
separately the coating may in most cases be removed as described 
under "amount of coating." The difference between the total 
ash and that in the body stock gives that present in the coating. 

If it is desired to calculate the original amount of filler used, 
or to make any computations regarding the minerals in the 
coating it is necessary to determine the nature of the mineral 
matters and in certain cases the amount of each present. This 
is rendered necessary because the different minerals lose different 
percentages of their weights in passing from the air dry to the 
ignited condition; some of the ground minerals used as fillers 
lose only about i per cent, clay shows a loss of around 1 2 per cent 
while crystalline calcium sulphate loses nearly 21 per cent. The 
complete quantitative analysis of an ash is a rather complicated 
process which can be carried out successfully only by a skilled 
chemist. The following simple tests may be of use where a com- 
plete chemical analysis is not considered necessary. 

Boil a little of the ash with water, filter and to the filtrate, 
acidified with hydrochloric acid,' add a few drops of barium chlo- 
ride solution. A white precipitate indicates sulphates. 

Warm a little of the ash with dilute hydrochloric acid filter 
and make slightly ammoniacal. Filter off any precipitate, which 
may have formed and add a little ammonium oxalate solution. 
A white precipitate indicates calcium. 

In order to be conclusive both these tests must be pronounced 
as small amounts of sulphates may be derived from the sizing 
materials and a little calcium is almost always present in clay. 

Evaporate a small sample of the ash to dryness after having 
moistened it with hydrochloric acid. Treat the dry residue with 
a little strong hydrochloric acid, take up a little of the moist 
material on a loop of platinum wire and hold it in a non-luminous 
gas flame. Calcium will impart a red color and barium a green 
color to the flame. If both are present the red color will show 
as soon as the wire is placed in the flame while the green will show 
with considerable persistence after the red has disappeared. 



SIZING MATERIALS 417 

Boil the material moistened with strong hydrochloric acid in 
the above test, with a little water, filter and add a slight excess 
of dilute ammonia. A whitish, flocculent precipitate indicates 
alumina from the clay used. 

No simple test for magnesia, indicating the presence of talc, 
asbestine or similar minerals, can be given, as the qualitative 
test for this element is one which requires more than the ordinary 
skill. 

Retention. By retention is meant that per cent of the entire 
loading material added to the beater which appears in the 
finished paper. To ascertain this determine the following facts: 

P = weight of pulp added in pounds 
C = weight of clay added in pounds 
A = per cent of ash in finished paper 

A p = per cent of ash in pulp 

W c = per cent of water of composition of clay 

M p = per cent moisture in pulp 

M c = per cent moisture in clay. 

The per cent of clay used would then be — - — > or with greater 

IOO C (i - Me) 

accuracy P(i-lf,) ' 

The retention may be calculated by the following formula?, 
the second being the more accurate. 

Retention = 



Retention = 



C (100 - A) 

iooP(A -K) 
C(ioo -A+K) 



In this last formula K is the per cent of filler not derived from 
the loading added; an average value, which may be applied in 
the above formula, is 0.50. 

Sizing Materials. In its broadest sense the term " sizing " is 
applied to a number of materials used in the beater, in the 
coating and in surface sizing, and satisfactory qualitative tests 



4 i 8 PAPER TESTING 

must be able to distinguish between these various substances 
and also to show whether a paper is tub (surface) sized or not. 

Starch may be, and frequently is, used for all three purposes 
and is applied either raw or cooked in the beater and cooked 
only in the other two cases. The universal test for starch is 
to apply a dilute iodine solution to the paper when a blue to 
violet color will appear if starch is present. It is well to" confirm 
this test by boiling some of the paper with a little water, filter- 
ing and testing the filtrate, after cooling, with a few drops of 
iodine solution. This is necessary because hydrocelluloses, 
which are only slightly soluble in boiling water, also give a blue 
color when brought into direct contact with iodine solution. 
Microscopic examination will show whether the starch granules 
have been burst by boiling or whether the starch was used with- 
out cooking. If the paper to be tested is torn so that it splits 
on the edge before being moistened with the iodine solution it 
is generally possible to tell whether it is surface sized or not. 
If it is surface sized only, the interior of the sheet will remain 
white while the surface will turn blue; if, however, consider- 
able starch was used in the beater, this is in part cooked and 
drawn to the surface by the heat of the driers so that the paper 
has the appearance of being surface sized when in reality it was 
not. Microscopic examination of the papers after treating with 
iodine will sometimes enable an opinion to be formed though 
it is seldom possible to prove positively in such a case whether 
the paper is surface sized or not. 

Casein may be detected in paper by moistening the sample 
with Millon's reagent and warming gently either over a flame 
or over an open steam bath. If casein is present a brick-red 
color will develop. In the case of coated paper in which much 
satin white is used, the alkali present determines the formation 
of a yellow color. In this case proof may be obtained by moist- 
ening the paper first with dilute nitric acid, to neutralize the 
alkali, and then applying the Millon's reagent as before; tested 
in this way satin white coated papers will give the usual red 
color. Casein may also be detected by boiling the paper with 



SIZING MATERIALS 419 

water and a few drops of ammonia, filtering and adding to the 
filtrate dilute acetic acid very gradually. Casein will precipi- 
tate when the solution becomes very faintly acid, but it may 
redissolve on adding a considerable excess. This test is also 
given, though usually less strongly, by rosin, so the precipitate 
should be tested with Millon's reagent to confirm the presence 
of casein. Casein is seldom used except in the coating; cases 
of surface sizing or of its use in the beaters are very rare. 

Glue is sometimes used as an adhesive in coating papers and 
in rare instances in the beaters; the better grades known as 
gelatines are used in surface sizing. If glue is present alone it 
may be detected by boiling the sample of paper in water, filter- 
ing if necessary, and adding a little dilute tannic acid solution; 
a grayish, flocculent precipitate indicates glue. Casein is also 
precipitated by tannic acid and the presence of starch prevents 
the precipitation of glue so that when either casein or starch is 
present there is apparently no means of proving the presence or 
absence of glue. 

Rosin is used almost exclusively in the beaters to impart 
waterproof properties to the paper. There is no single test of 
a simple nature which will demonstrate positively the presence 
or absence of rosin and any judgment regarding it must be 
based on the indications of a number of different tests. If a 
little ether is dropped onto a sheet of paper and allowed to 
evaporate there will be formed, in the case of rosin-sized paper, 
a ring of rosin at the edge of the zone where the ether evapo- 
rated. This will be absent in most unsized papers, and it will, 
of course, be formed in any paper which contains any ether 
soluble material besides rosin. 

Another test is made by boiling a little of the paper for a few 
minutes in glacial acetic acid and pouring the acid into a little 
distilled water. A pronounced turbidity indicates rosin, but a 
slight opalescence may be caused by other soluble substances 
and must be disregarded. 

A third test is that known as the Raspail reaction. If a drop 
of concentrated sulphuric acid be placed on the paper and a 



420 PAPER TESTING 

grain or two of sugar added a pronounced raspberry red color 
will develop with rosin-sized papers, while with unsized papers 
the color formed is brownish with only a trace of pink. This 
red color is also formed when albuminous materials are present 
so they must first be proved absent before the test can be con- 
sidered indicative of rosin. 

Rosin Determination. The amount of rosin in a sample of 
paper may be determined most accurately by the ether-alcohol 
method described by Sammet. 1 

"Cut five grams of paper into strips approximately one-half 
inch wide and fold them into numerous small crosswise folds. 
Place the folded strips in a Soxhlet extractor and fill with acidu- 
lated alcohol diluted to approximately 83 per cent, made by 
adding to 100 c.c. of 95 per cent alcohol 15 c.c. of acidulated 
water containing 5 c.c. of glacial acetic acid to 100 c.c. of dis- 
tilled water. Place the Soxhlet flask directly in the boiling 
water of a steam bath and extract by siphoning from six to 
twelve times, according to the nature of the paper. Wash the 
alcoholic extract of rosin, which may contain foreign materials, 
into a beaker and evaporate to a few cubic-centimeters on a 
steam bath. Cool, take up in about 25 c.c. of ether, transfer to 
a 300-c.c. separatory funnel containing about 150 c.c. of distilled 
water to which has been added a small quantity of sodium chlo- 
ride to prevent emulsion, shake thoroughly, and allow to separate. 
Draw off the water into a second separatory funnel, and repeat 
the treatment with a fresh 25-c.c. portion of ether. Combine the 
ether extracts, which contain the rosin and any other ether-soluble 
material, and wash with 100-c.c. portions of distilled water until 
the ether layer is perfectly clear and the line between the ether 
and the water is sharp and distinct. Should glue which is 
extracted from the paper by alcohol interfere by emulsifying 
with the ether, it may be readily removed by adding a strong 
solution of sodium chloride to the combined ether extracts, 
shaking thoroughly and drawing it off, repeating if necessary, 
before washing with distilled water. Transfer the washed ether 

1 J. Ind. Eng. Chem., 5, 732, Sept., 1913. 



CHLORINE 421 

extract to a weighed platinum dish, evaporate to dryness and 
dry in a water oven at from 98 to ioo° C. for exactly one hour, 
cool, and weigh. This length of time is sufficient to insure 
complete drying. Prolonged heating causes a continual loss 
of rosin. 

Paraffin Determination. Weigh out enough of the paper to 
give a weighable amount of paraffin, — one to two grams should 
be sufficient, — and place the sample in a Soxhlet extraction 
apparatus, or an Erlenmeyer flask, fitted with a reflux condenser. 
Cover with gasoline or carbon tetrachloride and extract until the 
paraffin is all dissolved; if the Erlenmeyer flask is used a second 
extraction with a fresh amount of solvent will probably be neces- 
sary. Evaporate the solution to dryness and weigh the residual 
paraffin. If there is a tendency for the paraffin to creep over 
the edge of the dish it may be more satisfactory to weigh the 
paper after extraction and consider the loss in weight as 
paraffin. 

Either gasoline or carbon tetrachloride is satisfactory from 
the standpoint of solvent power but the latter is to be preferred 
because of its non-inflammability. It is also superior to chloro- 
form because its fumes are not likely to produce anesthesia. 

Chlorine. As generally spoken of in the mill " chlorine " 
means free chlorine or more often hypochlorites. These are 
tested for in the stock in the beater by adding to a small sample 
of it a few drops of potassium iodide starch solution. If they 
are present a characteristic blue color will result, its depth being 
somewhat proportional to the amount of chlorine present. 

Where the finished paper is to be examined it is best to moisten 
it with distilled water on a glass plate and test it with starch 
iodide paper. 

It is sometimes desired to determine the total chlorine present, 
including that as hypochlorites, inorganic chlorides and organic 
chlorides. This may be accomplished by moistening a weighed 
sample of the paper with a solution of chlorine-free sodium car- 
bonate, drying it in a platinum crucible and then igniting cau- 
tiously until all the organic material is completely reduced to 



422 PAPER TESTING 

carbon. The soluble salts are then leached out and the chlorides 
in the solution are determined by titration with N/io silver 
nitrate solution. 

Free Acid Determination. Weigh 10 grams of the paper to be 
tested, tear into small pieces, place in a porcelain casserole and 
cover with a small amount of distilled water. Heat gently for 
an hour over water bath or electric hot plate. Pour off water 
and wash with small quantities of distilled water, adding same 
to water extract. Make up to ioo c.c. according to directions 
given on page 103 of Cohn's Indicators and Test Papers. 

The solution is then poured into a 100-c.c. Nessler tube (long 
form). A similar tube is filled with 100 c.c. of distilled water to 
which has been added two drops of the litmus solution. To the 
former is then added tenth normal standard solution of caustic 
soda until the color matches the sample. The acidity is then 
expressed in terms of S0 3 . 

Sulphur Determination. Sulphur may be present in paper in 
a number of different forms and from several causes. White 
papers may be toned with ultramarine, which nearly always 
contains sulphur, and which evolves hydrogen sulphide in the 
presence of alum or acid. The use of sodium thiosulphate as an 
antichlor or the presence of improperly prepared sulphite fibre 
may also account for the presence of sulphur compounds. 

The users of tissue paper for wrapping silver demand that the 
paper shall be free from sulphur and a method for its determina- 
tion, based on the stain produced on lead acetate paper, has been 
worked out as follows: 1 

The apparatus consists of a 500-c.c. round bottom flask with 
a neck about 2 ins. long and 1 in. in diameter. The mouth of 
this neck is ground to a flat surface and on this is placed a glass 
tube about 4 ins. long and an inch in diameter, the lower end 
of which is also ground flat to fit tightly upon the upper surface 
of the neck of the flask. The whole is so arranged that after 
placing a piece of filter paper between the two ground surfaces, 

1 Sutermeister: Pulp Paper Mag. Can., 15, 1917, 1021. 



SULPHUR DETERMINATION 423 

the tube and flask can be securely clamped together so that all 
gas generated in the flask must pass through the filter paper 
and then up through the superimposed glass tube. 

The procedure for the testing of tissue papers is as follows: 
A sample of 25 sq. ins. is taken and its weight determined. It 
is then shaken up in a wide mouth glass-stoppered bottle with 
10 c.c. of distilled water; when partial disintegration has taken 
place, another 10 c.c. of water is added and the shaking continued 
until the paper has been completely reduced to pulp. The 
larger part of the pulped mass is now transferred to the flask 
described above, and the residue which is left in the bottle is 
rinsed into the flask with a mixture of 10 c.c. of sulphur-free 
phosphoric acid and 20 c.c. of water. 

Prepare turnings from the highest grade, pure stick zinc, which 
must be free from sulphur and arsenic. Treat one gram of these 
turnings with 10 c.c. of a dilute solution of copper sulphate 
containing about 0.002 gram actual copper. After a few minutes 
all the copper will have deposited and the turnings are then 
thoroughly washed to remove every trace of zinc sulphate. 

The turnings are added to the flask and a wad of cotton 
inserted in its neck. Between the two ground glass surfaces is 
then clamped a piece of filter paper about 2 ins. square which 
has been perforated with small pinholes about | of an inch apart 
and which just before use is moistened with several drops of lead 
acetate solution. Finally a loose wad of cotton is placed in the 
tube above the paper. 

The flask is placed on the steam bath and allowed to stay, 
with occasional shakings, for an hour. The. filter paper is then 
removed from the neck of the flask and air dried. It is best 
compared with the standard test pieces by placing them side by 
side on a piece of white paper and covering them with a thin 
piece of clear, white glass. The standard test pieces are pre- 
pared by using sulphur-free cotton in the flask instead of the 
disintegrated paper and adding to this definite volumes of a 
very weak solution of sodium thiosulphate whose strength is 
accurately known. The sulphur-free cotton is prepared by 



424 PAPER TESTING 

boiling absorbent cotton in weak caustic soda solution and wash- 
ing thoroughly with distilled water. 

The sensitiveness of this test is such that the presence of 
o.oooooi gram of sulphur in the flask will give a distinct color on 
the lead acetate paper. From tests of a considerable number of 
papers which have been found satisfactory in actual practice it 
has been proved that tissue paper is safe for wrapping silver- 
ware if it does not contain more than 0.000002 gram of sulphur 
per 25 sq. ins. of paper (about 0.25 gram). 

In using this method certain precautions are necessary if 
reliable results are to be obtained. The sample to be examined 
must be kept away from all dust and laboratory fumes and in 
handling it in preparing the sample the fingers should be scrupu- 
lously clean. Any perspiration on the fingers will be sufficient to 
give an incorrect result and it was found by sad experience that 
if the fingers were run through the hair while handling the sample 
for analysis a strong test for sulphur was obtained. It is quite 
obvious that any sample which is submitted for tests should be 
taken from a freshly opened package of paper and that it should 
be handled as little as possible. To make a test of a sample 
which has been lying around an office for some time and which has 
been handled repeatedly is merely a waste of time. 

The purity of the zinc employed must be ascertained by very 
careful tests and the same is true of the phosphoric acid. Other 
acids should not be substituted for phosphoric acid unless they 
are first proved to be absolutely reliable and it has been demon- 
strated that sulphuric and hydrochloric acids are not entirely 
safe. 

The standard test papers, which are prepared with known 
amounts of sulphur, must be freshly made each time the test is 
carried out since they are not sufficiently permanent even when 
kept in tightly stoppered bottles in the dark. 

Amount of Coating. It is sometimes desirable to determine 
the percentage of coating on a sample of paper or the amount 
applied per ream. To do this cut a sample of some definite size 
and weigh in the air dry state; soak this sample for a few minutes 



GLUE OR CASEIN DETERMINATION 425 

in a dilute solution of ammonium hydroxide, remove it to a glass 
plate and loosen the coating by brushing carefully with a flat 
camel's hair brush moistened with the ammonia solution. Fi- 
nally wash in running water, air dry, and weigh. The difference 
in weight represents the coating removed. 

In some cases the coating is so thoroughly waterproofed that 
this treatment fails to remove it; in such cases there is no known 
method for determining its amount. Where the coating is partly 
waterproofed it may be desirable to increase the strength of the 
ammonia or to warm it slightly. Where the coating is not easily 
removed the brushing must be done with great care lest a con- 
siderable loss in weight be caused by removal of fibrous material. 
It is sometimes a question of judgment as to whether a greater 
error is caused by failure to remove traces of coating or by 
rubbing off some of the fibres. 

Glue or Casein Determination. There is apparently no quan- 
titative method known for the determination of these substances 
when they are present together. Both materials contain nitro- 
gen. If only one be present and the nitrogen content of the 
original material as added to the paper be known then by means 
of the nitrogen determination the content of glue or casein may 
be estimated. 

For the determination of nitrogen weigh out from three to five 
grams of the paper, cut into small pieces and place in a Kjeldahl 
digestion flask. Add 10 grams potassium sulphate, 0.7 gram 
mercury and 25 c.c. of concentrated sulphuric acid; place the 
flask in an inclined position in a hood with a good draft and heat 
below the boiling point of the acid until frothing has ceased. 
Increase the heat until the acid boils briskly and continue the 
digestion until the solution is colorless or pale straw yellow. 
Allow the contents of the flask to cool and add 30 c.c. of a 4 per 
cent solution of potassium sulphide. Next add 50 c.c. of caustic 
soda solution (saturated solution), or enough to make the reaction 
strongly alkaline, pouring it carefully down the side of the flask 
so that it does not mix with the contents. Connect the flask at 
once with the condenser, shake to mix the contents of the flask, 



426 PAPER TESTING 

and distil until all ammonia has passed over. Collect the dis- 
tillate in a flask containing a known volume of standard acid, and 
at the end of the test titrate the excess of acid with standard 
alkali, using sodium alizarin sulphonate or methyl red as indica- 
tor. The end of the condenser tube should dip below the surface 
of the acid, the distillation should require about 45 mins. and the 
distillate should amount to about 200 c.c. If a few pieces of 
granulated zinc or pumice stone are added to the distillation 
flask bumping during the distillation may be avoided. 

As a check on the purity of the reagents a "blank test" should 
be made using the same amounts of chemicals as in the regular 
test but adding no paper. 

Substract the volume of alkali required to neutralize the dis- 
tillate from the volume required by the blank; the difference is 
the number of cubic centimeters of standard alkali equivalent to- 
the ammonia. This number of cubic centimeters of tenth nor- 
mal alkali multiplied by 0.0014 gives the grams of nitrogen in 
the sample taken. To convert this to casein multiply by the 
factor 6.3, and for glue use the factor 5.6. Since the percentage 
of nitrogen varies in different lots of casein and glue these factors 
should be determined, wherever possible, on the actual materials 
used in the paper being tested. 

Unbleached Fibres. Besides the microscopical method de- 
scribed elsewhere it is possible to detect unbleached sulphite fibre 
by chemical means. If a sheet of paper containing a small 
amount of unbleached fibre is moistened with Millon's reagent 
and then warmed in the steam escaping from a steam bath it will 
be found that the unbleached fibres will show up very distinctly 
as brownish hairs. If no unbleached fiber is present the brown 
hairs are absent. From the proportion of fibres stained brown 
it is possible to make an approximate estimate of the amount of 
unbleached fibre present, provided its quantity is not large. 
Where the sheet is mostly unbleached, or where groundwood 
is present in considerable amount, the entire surface becomes 
brown and no estimate of the proportion of unbleached fibre can 
be made. 



GROUND WOOD PULP 427 

Groundwood Pulp. For the qualitative determination of 
groundwood a number of stains are available and find quite 
general application. 

Aniline sulphate stains groundwood a yellow color, though the 
test is not quite so sensitive as that with phloroglucinol. The 
aniline sulphate solution should be prepared by dissolving 
5 grams in 50 c.c. of distilled water and acidulating with one drop 
of concentrated sulphuric acid. 

A very satisfactory stain is made by dissolving 1.0 gram of 
paranitroaniline in 405 c.c. of distilled water and 30.5 c.c. of 
sulphuric acid (sp. gr. 1.84). With groundwood this gives an 
intense orange color which develops without drying the sample. 
This stain possesses an advantage over phloroglucinol in that the 
acid is not volatile and that it does not deteriorate so rapidly. 

One of the most generally used stains is prepared by dissolving 
5 grams of phloroglucinol in a mixture of 125 c.c. of distilled 
water and 125 c.c. of concentrated hydrochloric acid. This solu- 
tion should be kept in the dark as light affects its staining proper- 
ties to some extent. With groundwood this stain causes a ma- 
genta color, the depth of which is approximately proportional 
to the amount of groundwood present. A very light shade, 
however, does not necessarily prove the presence of groundwood, 
as partly cooked jute, undercooked unbleached sulphite and 
some other fibres are also"slightly colored. 

The reaction with phloroglucinol has been employed by Cross, 
Bevan, and Briggs 1 as the basis of a quantitative method for 
estimating groundwood. The necessary solutions are: 

1. 2.5 grams of pure phloroglucinol dissolved in 500 c.c. of 
hydrochloric acid, sp. gr. 1.06. 

2. 1 c.c. of 40 per cent formaldehyde in 500 c.c. of hydrochloric 
acid, sp. gr. 1.06. 

The paper under examination should be rasped to a loose pow- 
der but size need not usually be extracted. Two grams of the 
powdered sample are dried at ioo° C, weighed, transferred to a. 
dry flask and covered at once with 40 c.c. of phloroglucinol solu- 

1 Cross, Bevan and Briggs: Papier Ztg., 32, 1907, 4113 and 4479. 



428 PAPER TESTING 

tion. The flask is stoppered, shaken, and allowed to stand 
several hours or best over night. The solution is next filtered 
through a very little cotton placed in a funnel and 10 c.c. are 
measured out for titration. This is diluted with 20 c.c. of hydro- 
chloric acid (sp. gr. 1.06), warmed to about 70 C. and the 
formaldehyde solution added from a burette in lots of 1 c.c. at a 
time. Allow to stand two minutes after each addition and then 
remove a drop without filtering and place it on a strip of partly 
sized news paper. After ten seconds shake the drop off and see if 
a red color is produced; if it is, add more formaldehyde solution 
and toward the end of the reaction reduce the amount added each 
time to 0.25 c.c. Non-development of a red color indicates the 
end of the reaction. The test paper is sensitive to a solution of 
one part of phloroglucinol in 30,000. 

A' control test should be made with 10 c.c. of the phloroglucinol 
solution in exactly the same way and the absorption of the 
groundwood calculated from the difference of the two titrations. 
It should be based on the dry material taken for analysis. 

In carrying out this test it is essential that pure phloroglucinol 
be used and it is well to obtain a considerable supply so that its 
uniformity may be assured. The proportion of sample to phloro- 
glucinol solution must be kept constant and the temperature 
must be maintained at 70 C. during the titration. 

The absorption numbers of various fibres have been found to 

be as follows: Percent 

Groundwood 7. 87-8. 15 

Groundwood, brown 5. 52 

Sulphite, bleached o. 90-1. 00 

Sulphite, unbleached o. 90-1. 03 

Esparto o. 50 

Cotton o. 20 

Assuming an absorption number of 8 per cent for groundwood 
and 1 per cent for sulphite then 

ry IOO (P — I.o) 

ti = — 1 

8.0 — I.O 

where H = per cent of groundwood 

<P = absorption value of dry ash-free fibre in sample. 



CHAPTER XVI 
PRINTING 

In spite of its title this chapter is not a dissertation on the art 
of printing but is rather a collection of facts, intended to throw 
a little light on the relation of the paper maker, the printer and 
the ink maker. It is frequently the case that no one of the three 
fully understands the troubles of the others and this lack of 
knowledge prevents the cooperation which is necessary if the 
greatest progress is to be made. Fortunately it is becoming 
more frequent to find mutual assistance taking the place of un- 
justified criticism and it is this spirit of helpfulness which has 
enabled many of the following notes to be collected. Necessarily 
they relate chiefly to the use of book and coated papers, since 
it is upon these papers that by far the greatest amount of fine 
printing is done. 

Printing may be defined as "the reproduction of designs, char- 
acters, etc., on an impressible surface by means of an ink or a 
pigment (generally oily), applied to the solid surface on which 
they are engraved or otherwise formed." 1 The only "impres- 
sible surface" which need be considered here is the paper. Ac- 
cording to the method of preparation of the "solid surface" the 
various printing processes may be classed under three headings: 
(i) relief; (2) intaglio; and (3) planographic. The relief proc- 
esses are those in which the printing surface stands up above the 
surrounding ground; of this group the half-tone is the most im- 
portant representative. Intaglio engravings are those in which 
the design to be printed lies below the surrounding surface of 
the plate; the depressed lines or dots hold the ink which is trans- 

1 Century Dictionary. 
429 



430 PRINTING 

ferred to the paper after the surface of the plate has been wiped 
clean. The old-fashioned steel-engraving is typical of the intaglio 
process. Planographic processes are those in which the printing 
is from a flat surface, neither raised above, nor depressed below, 
the surrounding ground. Lithography with its flat stone or metal 
plate is typical of planographic processes. 

Half-Tone Plates. For the preparation of half-tones a 
"screen" is necessary. This is prepared by coating a sheet of 
glass with a wax composition and then ruling diagonally upon it 
fine parallel lines at exactly equal distances from each other. The 
plate is then treated with hydrofluoric acid, which etches the 
glass wherever the diamond point has removed the wax, and 
after cleaning the plate an opaque, dark pigment is rubbed into 
the lines. Two such plates are sealed together face to face, with 
the rulings at right angles, to form the finished screen. The dis- 
tance between the lines varies from 50 per inch for very coarse 
work to 300 for the finest. 

What is termed a screen negative is prepared by placing this 
screen in a camera, in front of and near the plate, but not in direct 
contact with it, and then photographing, through the screen, the 
picture, drawing or photograph to be reproduced. The lines 
prevent the passage of light, and the resulting negative consists of 
innumerable dots separated by the unexposed spaces which were 
covered by the lines. 

The metal plate which is to form the half-tone block is carefully 
planished, sensitized with a mixture of gelatine and bichromate of 
potash, dried, and exposed under the screen negative just as in 
ordinary photographic printing. Copper is used for the best 
plates while zinc is employed in cheaper work. The exposed 
plate is then washed in water which dissolves the gelatine film 
wherever it has not been exposed to light. This gelatine picture 
is heated and burnt onto the metal like an enamel which protects 
the metal at these points during the next step which is etching. 
This is done by treating the plate with ferric chloride solution 
which dissolves away the copper where it is not protected by the 
enamel, thus leaving the picture in relief. In order to produce 



HALF-TONE PLATES 



43 1 



the best results the plate must be re-etched locally and it is in 
this operation that skill and judgment are most necessary on the 
part of the plate maker. The following table shows the standard 
depths for half-tone plates in thousandths of an inch. 



Tone values 


55;line 
zinc 


85-line 
zinc 


100-line 
zinc 


100-line 
copper 


120-line 

copper 


133-line 
copper 


ISO-line 
copper 


175-line 
copper 


High lights 

Middle tones 

Shadows 


8 
S 
3 


4.6 

3-i 

2 .2 


3-2 
2 .2 
1-4 


2.6 
1.8 
1 .0 


2-5 
1-7 
0.9 


2-3 
1.6 
0.9 


2 .2 

1-4 
0.9 


1.8 

1 .0 
0.6 



Original plates are seldom used where any large number of 
impressions are to be made as they soon wear out, necessitating 
the making of entirely new plates ; the use of electrotypes obviates 
this difficulty. These are prepared by coating the original with 
a thin film of the finest graphite and then taking an impression of 
its surface in wax or gutta-percha. The graphite prevents 
sticking and allows the plate to be removed from the wax, which 
is then placed in a bath of copper sulphate and coated electro- 
lytically with a film of copper. Deposit of copper may be con- 
tinued until it becomes thick enough to use as a plate or a thinner 
film may be backed up by type metal. This process allows any 
number of electrotypes to be prepared from the same original, 
which insures a sufficient supply of plates for even the largest 
editions. Where excessive wear is expected they are sometimes 
faced with steel or nickel by electrolytic means. 

For three color work three half-tone blocks have to be prepared, 
one for yellow, one for red, and one for blue. Three separate 
photographs are taken through ray filters; the first of these 
absorbs all rays except those coming from yellow portions of the 
picture, the second does the same for red and the third for blue. 
From these three photographs three half-tone blocks are made 
in the usual way except that the screen is turned at a slight angle 
so that when the plates are printed one over the other the dots 
will not fall exactly in the same place but will form little patches 
of color side by side. 



43 2 



PRINTING 



Lithography. The stones used for lithography are certain 
porous limestones which possess the property of absorbing either 
water or grease but which will not take up a greasy ink wherever 
they have been moistened. The surface of the stone is prepared 
by grinding it with emery or sand, using a small stone or a cast 
iron levigator moved in circles all over the surface, until it is 
perfectly flat. The next operation is polishing with pumice 
stone to remove sand scratches and this is then followed by a final 
polishing with a " snake-stone." This completes the preparation 
of the stone for some kinds of work but for others the surface has 
to be grained. This is accomplished by hand by going over it 
with graining sand and a muller or mechanically by sprinkling it 
with sand and rolling it with glass balls. 

The design may be placed upon the stone in two ways; it may 
be drawn on the surface directly by a pen or a brush or by means 
of a greasy crayon, known as "chalk"; or it may be transferred 
to the stone from a design prepared upon suitable transfer paper. 
When the drawing is made directly upon the stone it has to be 
in reverse so that the final print may be in the proper position. 
The next operation is a treatment with a gum arable solution, 
followed, after drying and washing, by rolling up with ink. Cor- 
rections are made by a scraper and dirt is removed by acid and 
the stone is etched by dilute nitric acid, which acts only on those 
portions which are not protected by ink. After etching the 
stone is again inked, gummed and set aside to dry; when wanted 
for printing the gum is washed off and the surface of the stone 
allowed to become saturated with water. 

The principles of lithography, as very briefly outlined, are also 
applied to modified processes such as printing from plates of zinc 
and aluminum and also in the more recent offset, process. 

Paper for Different Types of Printing. The kind of paper 
which should be used on any job depends on a number of factors 
which include the kind of work being produced, the skill of the 
printer, the artistic education of the customer and finally the 
price which he is willing to pay. It is frequently the case that the 
quality of the paper is determined by the illustrations which it 



PAPER FOR DIFFERENT TYPES OF PRINTING 433 

is necessary to use since type matter can be printed successfully 
on any paper. 

Half-tones prepared from very coarse screens may be used on 
even such poor paper as news print but the results obtained can 
hardly be called artistic, though they serve their purpose. As the 
paper becomes better and its surface smoother the screen may 
be torrespondingly finer. It is difficult to establish definite 
limits for the screen which may be used successfully with any 
class of papers since papers of the same class vary considerably 
in finish from time to time and according to the mill in which 
they are made. Considering book papers, upon which most of 
the fine printing is done, the following may be taken as approx- 
imately the limit of fineness for the screen which may be used 
with good success. 

Lines 

Machine finish book .■ 1 20 

Super and English finish 133 

Imitation coated 150 

Dull and semi-dull coated 133 

High finish coated 175 

For the best results in printing half-tones, the surface of the 
paper must be such that every dot is perfect. If the paper is 
rough many of the dots will fall upon the elevated portions, 
where they will print, but enough will come over depressions, 
where they will not touch the paper, to give a decidedly gray 
and irregular print. The avoidance of such irregularities is 
the chief argument for the use of coated papers. 

The rotogravure process uses a copper cylinder on which 
the illustration is printed from a positive prepared without 
the use of a screen. The etching is similar to that of the half- 
tone plate but is entirely mechanical. After inking the excess 
is removed from the surface by a doctor which leaves the de- 
pressions filled with ink. The paper is then pressed into these 
inked portions by means of a rubber roller. This process pos- 
sesses the advantage that papers of the poorest quality give 
very beautiful results; even very low grade news print can be 
depended on to give illustrations with remarkable depth of tone. 



434 PRINTING 

For lithographic work the paper should lie flat in order to 
avoid wrinkles during printing. The filler used in plain paper 
must be free from gritty particles as these cause etching of 
the stones or plates. Where coated paper is employed, the 
adhesive used in the coating must be such as to give it water- 
proof properties, or rather .insolubility, so that the dampness 
will not cause the coating to come off. If the printing is from 
zinc or aluminum plates the paper must be free from any chemi- 
cals which might dissolve and cause etching of the plates. 

Paper used for offset printing is generally of an antique finish 
though coated paper can also be used. This process was made 
possible by the use of metal plates. It uses less ink than the 
ordinary lithographic process and causes less wear on the plates 
as the latter do not come in contact with the paper but only 
with a rubber blanket which is used to transfer the ink from 
the plates to the paper. Paper for this process must be well 
sized and have a firm, hard surface, free from fuzz. If the 
paper is unsized, the damp blanket tends to remove fibres and 
dust which are transferred to the plates and cause fill-up troubles 
and dirty prints. Freedom from wire and felt marks and a 
neutral reaction are desirable properties, and the sheets must 
be perfectly flat so that wrinkles may not form in passing through 
the press. Stretching of the sheet under pressure must also be 
avoided as much as possible as it also causes wrinkles to form. 

Choice of Inks. The selection of a proper ink for the paper 
which is to be used is generally the key to success in that par- 
ticular job. There are comparatively few general rules to fol- 
low and it is largely a question of skill and experience on the 
part of the printer. Even if he uses good judgment in the 
choice of an ink type, his results may turn out poor, for he is 
almost entirely at the mercy of the ink maker who may use* 
inferior raw materials with little fear of detection. Ink is a 
very complex mixture which it is practically impossible to an- 
alyze with any degree of accuracy or completeness; moreover 
the figures which can be obtained are not easy of interpretation. 
For these reasons it is good policy to obtain inks from reliable 



DEFECTS 435 

manufacturers who are known to turn out good products and 
who are building up or maintaining good reputations. 

Inks are composed chiefly of pigments and oily carriers or 
vehicles. These range from high grade varnishes in the inks 
for engravings down to low grade oils for the cheap inks used 
for news print. To these ingredients are added numerous other 
materials such as driers, softeners, oil soluble colors, etc., each 
of which imparts certain properties to the ink and makes it 
suitable for some particular kind of work. The ink for printing 
newspapers, for example, must dry by penetration and not by 
oxidation, because the rapidity with which the paper is handled 
allows no time for oxidation to take place. At the other ex- 
treme is the ink for engravings, such as letter heads, etc., in 
which a very stiff varnish is used so that the ink will stand up 
above the surface of the paper and dry entirely by oxidation. 
Between these two limits there are all kinds of inks made up 
for all kinds of printing; opaque inks for colored papers so 
that the color of the paper will not show through; transparent 
colored inks for process work; double tone inks; those which 
dry glossy and those which dry with a dull finish, and many 
others for special purposes. 

Defects. It has been stated by one who has had much ex- 
perience in both the paper and the printing industries, that 
fully 70 per cent of the criticisms against paper are due to 
troubles caused by inferior or inappropriate inks. In addition 
to the selection of an unsatisfactory ink, there are the troubles 
caused by the printer who finds his work defective in some way 
and attempts to improve it by the addition of some material to 
his ink. While the "dope" used may cure the trouble, it is, at 
the same time, likely to cause defects in some other, and totally 
unexpected, quarter. The modification of inks is something 
which should be done by, or under the direction of, a man who 
has had years of experience . and even under those conditions 
it is apt to do more harm than good. 

There are, of course, many defects which may be present in 
the paper and which may cause the printer serious trouble. 



436 PRINTING 

Some of these are so obvious that they hardly need mentioning. 
Among these would be classed fuzz on the surface, and trimming 
dust from the edges; these cause the filling up of cuts and type 
and may give the appearance of picking in half-tone illustra- 
tions or heavy blacks. Such defects make it necessary to wash 
up frequently if good work is to be turned out and in the case 
of coated papers often lead to their rejection as weak coated 
when in reality the coating was amply strong. Not all cases 
of fuzz, however, can be laid entirely to the paper criticized, as 
an examination of the fuzz collected from the press usually 
shows the presence of some wool and silk fibres and sometimes 
it is found to be composed largely of fibres which were not used 
in that particular paper. Curling, wavy edges or a cockly sur- 
face are also very readily detected in paper though not always so 
easily cured. They may be caused by too prolonged beating, 
unsatisfactory drying on the machine, defects in the calenders, 
or variations in the humidity of the surrounding air. In the 
last case the paper usually becomes flat again if it is stored in 
thin layers for a sufficient length of time for it to come to equi- 
librium with its surroundings. 

Lumps in paper are a fruitful source of complaint and are 
often, though not always, justly blamed on the paper. If large 
or thick they may seriously injure the plates or even ruin them, 
necessitating the preparation of new ones. Lumps may be 
caused by any number of things; if they are an integral part of 
the paper, they are frequently from the growth of slime in the 
pipes or chests, or from strings of fibre which collect on the 
screen plates and finally drop off, or from rolls of stock which 
break away from some doctor on the presses or driers. These 
are the fault of the paper and nothing else, but there is another 
class, the blame for which cannot be so definitely placed. This 
includes lumps which have become fastened to, or pressed into, 
the surface of the paper after the latter has been completely 
dried. Here there is always the possibility that they came 
from something in the press-room just as well as from a defect 
in the paper mill. Among the complaints on record, are those 



DEFECTS 437 

relating to lumps composed entirely of fibres and printing ink; 
here the fibres might have been contributed by the paper, but 
the ink must have come from the press-room. In another case, 
lumps of starchy material resembling cake were complained of; 
some boy may have thrown part of his lunch at a fellow work- 
man, but it might just as well have been in the press-room as 
in the paper mill. In the case where the complainant stated 
that lumps of metal were present in the paper and on examina- 
tion they were found to have the appearance and chemical 
composition of electrotype metal it was reasonable to exonerate 
the paper mill. 

Complaint is often made that the ink strikes through the 
paper and causes staining on the other side. With very fluid 
inks of the double-tone type it is possible to make them strike 
through, but it can be done only by using an excessive amount, 
far more than would ever be used even on the heaviest cuts. 
It has been stated by one ink manufacturer that with paper 
as heavy as 25 X 38 — 70, the ink is not made which will 
strike through. In nearly all such complaints the trouble can 
be proved to be offset provided enough of the printed sheets 
are submitted. In some the offset will coincide so exactly with 
the print that it might easily be taken for soaking through, but 
in others it will be found to be displaced uniformly to one side 
of the cut, indicating that it did not strike through but that it 
is an offset from the sheet below upon which the sheet in ques- 
tion did not fall exactly true. At times the fact that it is an 
offset can be proved by finding traces of the pigment portion of 
the ink upon the stained paper. Even though the oily part 
might strike through, it is hardly conceivable that the solid 
pigment could be made to do so. Tearing the paper so that 
it will split and expose the inner part of the sheet will prove 
that the pigment has not penetrated far into the paper and in 
most instances will show that the stain is wholly upon the 
surface. 

Offsetting is a well-known phenomenon and is avoided in 
the press-room by slip-sheeting. There are certain well-recog- 



438 PRINTING 

nized types of work in which slip-sheeting is necessary and 
others in which it is not required, and so long as papers fall in 
their proper classes, offsetting cannot be considered a defect 
either of the paper or the ink. There are occasional abnormal 
cases, however, in which either the paper, or the ink, or both, 
may be to blame. If the paper is finished and packed very 
dry, handling it may cause so much electrification that the 
sheets will cling to each other as they are piled up after printing. 
This close contact tends to increase offsetting. Electric neu- 
tralizes are a great help in eliminating electricity from the 
paper, while the gas flame arrangement attached to the press 
in such a manner that the printed sheet passes over it has a 
tendency to prevent offset. Both these devices are in general 
use in the large printing plants. 

Excessive atmospheric humidity, which greatly delays the 
drying of the ink, is also a cause which contributes toward 
offsetting. The use of slow drying inks and the employment 
of papers which are so hard sized with animal sizing that the 
ink does not readily penetrate both tend to increase the trouble, 
while greater porosity of the paper decreases it. In general it 
may be said that the majority of coated papers will offset seri- 
ously if not slip-sheeted, while with machine finish and antique 
papers such precautions are seldom necessary. 

The drying of the ink is sometimes so slow that complaint is 
made regarding the quality of the paper. The only qualities 
in the paper which are known to retard drying are lack of poros- 
ity, and in the case of coated paper too much of certain oils or 
waxes in the coating. On the other hand, atmospheric condi- 
tions may hinder drying or the composition of the ink may be 
at fault; it is a well-known fact that the drying of an ink can 
be very greatly changed in either direction by the proper ad- 
justment of the ingredients. Poor drying sometimes results 
during color work because of the so-called "crystallizing" of 
the yellow which is printed first. This trouble occurs because the 
yellow dries in such a way as to prevent the penetration of the 
other colors which consequently remain on the surface and dry 



DEFECTS 439 

very slowly. This defect in the ink can be easily corrected if it 
is discovered before the job is completed, yet this is not always 
done and then the paper gets the blame unjustly. Not only 
is this true, but at times the printer complains to both the paper 
maker and the ink manufacturer in order to make sure of a 
rebate from one or perhaps both sources. 

Picking is a defect of coated paper caused by a deficiency of 
adhesive in the coating. This weakens the adhesion of the 
mineral matter in the coating to the body stock to such an extent 
that it is overcome by the ink and the coating is removed in 
places causing white spots in the print and also fouling the 
plates or type. As already noted, some complaints of picking 
are due to dirt which collects on the plates and prevents the 
ink from coming in contact with the paper; these are easily 
distinguished from true picks by examination under a strong 
lens or a microscope, as they show that the coating is intact and 
not ruptured as it is when picking has taken place. Picking is 
usually the fault of the paper maker though this is not always 
true. If too tacky an ink is used any paper can be made to 
pick, no matter how strongly the coating may be sized. The 
selection of an ink of the proper consistency, or the adjustment 
of its consistency to suit the paper, is therefore of very great 
importance in using coated paper. The temperature of the 
press-room and the ink also influence the results very greatly. 
Most inks are ground in No. i yarnish and will work properly 
at 70 F. At this temperature No. 1 varnish has as much tack 
as No. o varnish at 6o° F., No. 2 varnish at 8o° F. or No. 3 
varnish at 90 F. The colder the ink the more tacky it be- 
comes, hence picking is more frequent on Monday mornings 
when starting work. Defects from this cause should not be 
blamed on the paper since the trouble disappears when normal 
conditions are once more established. 

A result somewhat similar to the picking on coated paper is 
found very rarely in plain papers. This is caused by dry froth 
from the wet end of the paper machine which gets onto the 
surface of the paper -as it is being formed but does not become 



44-0 PRINTING 

thoroughly incorporated with it. On drying and calendering 
these bits of froth are smoothed down so that they do not show 
except on very careful inspection, yet they do not adhere very 
firmly to the sheet and are readily removed by the inked plate 
causing a white spot closely resembling those where coated 
paper has picked. 

In lithograph work it is claimed that the paper sometimes 
causes the ink to smut or to show slightly where there should 
be white surfaces only. This is said to be due to chemicals in 
the paper which act on the stones or metal plates and cause 
them to take a little ink where there should be none. For this 
reason it is well to avoid the presence of water-soluble sub- 
stances which can in any way affect the plates. In some cases, 
however, this smutting is not the fault of the paper but of the 
ink which may be made of dyes or lakes which are partly sol- 
uble in water and are therefore taken up as very light tints by 
that portion of the stone which has been moistened This is 
particularly likely to happen with inks in which eosine or similar 
dyes have been used. To prove the presence of such water- 
soluble colors in the ink, a piece of the printed sheet may be 
placed between sheets of moist, white blotting paper and pressed 
for some time in a copying press. If water-soluble dyes were 
used, a distinct offset will be present on the blotter. 

Another defect of coated paper which is not strictly one of 
printing, but is closely allied to it, is that of brittleness or poor 
folding qualities. This can be avoided to a considerable extent 
by the proper selection and beating of the fibres for the body 
stock and by the use of as little coating as is consistent with 
obtaining the proper printing surface. Much can be done to 
avoid the cracking of the surface by the careful handling of 
the sheets in the folding and stitching machines. Where possible 
the fold should be made with the grain of the paper and opera- 
tions should be conducted in as damp an atmosphere as possible 
since the damper the paper the less it will crack on folding. 

Grayness of the cut or filling-up of the half-tone screen are 
things which are occasionally blamed to the paper. The gray- 



DEFECTS 441 

ness of an illustration is almost entirely a question of ink selec- 
tion or adjustment; it may be possible to overcome it by using 
more ink, provided too much is not used, or perhaps another 
ink can be substituted. In case the ink needs to be reduced a 
black ink of the desired consistency should be used rather than 
a varnish, for the latter may diminish the covering power of 
the pigment to such an extent that the cut will appear gray. 
Reduction with a liquid is also more likely to result in filling 
up the plates, which, necessitates frequent clean ups. Grayness 
may also be caused by too porous a coating which absorbs too 
much of the ink and leaves so little on the surface that it is not 
well covered. The froth pits which are sometimes present in 
poorly coated paper may, if present in too great numbers, 
cause gray prints either locally or throughout the cut. These 
pits are caused by small bubbles which keep the coating away 
from the spot which they occupy and when they finally break 
leave a depression or pit in the coated surface. These are so 
much lower than the general surface that the ink is not forced 
into all of them and the result is a white spot where there should 
be a half-tone dot of ink. 

Filling up of the half-tone plates results in a muddy cut in 
which detail is lacking. This is most frequently the result of 
improper selection of ink and can often be corrected by sub- 
stituting a different quality. Occasionally the paper may be 
at fault if its surface is at all inclined to be dusty or to allow 
very minute fragments to break away and become mixed with 
the ink. 

In some cases an ink is supposed to dry with a dull, lustre- 
less surface instead of the usual gloss; such inks are largely 
used on the dull and semi-dull finish papers. When using 
such inks it is sometimes observed that the completed print 
has a mottled effect, part of the surface being dull, while the 
rest is shiny. This shiny part is generally distributed quite 
regularly in patches of moderately uniform size, the edges of 
which gradually shade off from the glossy to the dull surface. 
This mottled effect is due to the fact that part of the sheet is 



442 PRINTING 

less absorbent than the rest and in these less absorbent spots 
the ink is obliged to stay upon the surface and dry like a var- 
nish. The exact reason for this trouble has not been fully de- 
termined, but it probably goes back to irregular formation on 
the paper machine. If the fibres are more or less bunched up 
they will give a surface with hills and hollows; this may be 
reduced to a plane surface by calendering but the density of 
the sheet must vary according to the amount of compression it 
has undergone and its ability to absorb ink will vary corre- 
spondingly. Where coating is applied to a "wild" sheet it tends 
to be thicker in the hollows than on the elevations and when it is 
calendered there is again a considerable variation in density 
and porosity. It is quite probable that local variations in the 
sizing of the sheet are caused by the weave of the drier felt 
exerting more or less pressure on the sheet as it is dried. When 
such a sheet is coated the adhesive is absorbed more completely 
by the slack-sized spots and is held upon the surface where it is 
harder sized. When it is calendered it appears to have a uni- 
form finish, but wherever the sizing is harder than elsewhere 
the ink will not penetrate and will dry with a gloss. .It is abso- 
lutely certain that a high gloss does not necessarily mean a 
good printing surface although the two are not necessarily 
incompatible. 

Closely connected with the mottled effect is the excessive 
spread of the double-tone inks when they are used on certain 
papers. The amount of adhesive used in the coating has much 
to do with this for if the coating is porous the ink is absorbed 
without allowing any sidewise spreading of the oil, while if it 
is non-absorbent, because of too much adhesive, the ink will 
spread to an excessive extent. 

In color work where a number of impressions are made at 
intervals the question of register is very important. If the 
size of the sheet changes between impressions.it is practically 
impossible to make the two colors coincide and a defective 
job results. This is often claimed to be the fault of the paper 
by printers who believe that the paper maker can treat his 



DEFECTS 



443 



product so that it will not change dimensions with changing 
atmospheric conditions. As an actual fact very little can be 
done by the paper maker to cure this trouble since it is just as 
inherent in paper to stretch when dampened as it is for wood to 
swell when exposed to moisture. If the paper is sent out con- 
taining the average amount of moisture which it would be 
expected to contain under the conditions of the average print- 
ing shop, the paper maker may be considered to have done his 
best and the rest is up to the printer. Seasoning the paper in 
the press-room to bring it to equilibrium with its surroundings 
is an excellent precaution, particularly where constant humidity 
conditions are maintained in the press-room. If the shop win- 
dows are kept open so that outside changes are transmitted to 
the paper, good register is a question of good luck or of waiting 
before making the second impression until the same weather 
conditions prevail as when the first color was applied. With 
commercial work, where the job must be completed at a definite 
time, waiting is out of the question, so the single factor of luck 
may be said to be the important one. Both temperature and 
humidity control in the printing shop are strongly recommended, 
if much color work is to be done. The temperature, if it changes 
materially, will alter the size and relative position of the plates 
enough to cause trouble, while the humidity has a very great 
effect on the paper. It is interesting to note that in shops 
where air conditioning systems are installed color work can 
be done successfully during periods of weather which completely 
shut down shops of the ordinary type. 



APPENDIX 



Solubility of Aluminum Sulphate 

(Poggiale) 

ioo parts water dissolve (a) parts Al 2 (S0 4 ) 3 and (b) parts Al 2 (S0 4 ) 3 • li 
H 2 at 



0° 


IO° 


20° 


30° 


40 


3i-3 
86.85 


33-5 
95-8 


36.15 
IQ7-35 


40.36 
127.6 


45-73 
167.6 



6o° 



59 09 
262 .6 



73-14 
467-3 



89.11 
1 13 2 .00 



Influence of Temperature on Density of Black Liquor from the 
Sulphate Process 

(C. Moe) 



Degrees 
F. 


Specific 
gravity 


3aume S P ec i fic 
rsaume g^^y 


Baume 


Specific 
graviiy 


Baume 


Specific 
gravity 


Baume 


200 








I . 0800 


10.7 






190 




.... I . 0080 


I 


2 


I . 0840 


II .2 


I .2560 


29.6 


180 


O . 9800 


.... I .0120 


I 


7 


I.0880 


II. 7 


I . 2600 


29.9 


170 


O.9840 


.... I .0160 


2 


3 


I .0920 


12 .2 


I .2640 


30.3 


160 


O.9880 


.... I .0200 


2 


8 


I .0960 


12.7 


I . 2680 


30.7 


I50 


O.9920 


.... I .0230 


3 


3 


I -0995 


13- 1 


I .2720 


31.O 


140 


O.9950 


.... I .0260 


3 


7 


I . 1030 


13-5 


I .2760 


3i-4 


130 


O.9980 


.... I .0290 


4 


1 


I. 1065 


14.0 


1-2795 


3i-7 


120 


I .OOIO 


0.2 I.0320 


4 


5 


I . 1095 


14-3 


1 . 2830 


32.0 


no 


I . 0030 


0.4 I.0340 


4 


8 


I.II25 


14.7 


1.2865 


32.3 


IOO 


I . 0050 


0.7 I.0360 


5 





I-H55 


150 


1 . 2900 


32.6 


90 


I .0070 


1.0 1.0380 


5 


3 


1 .1180 


15-3 


1 -2935 


32-9 


80 


I .0080 


1.2 I.O4OO 


5 


6 


1. 1205 


15-6 


1 .2970 


33-2 


70 


I . 0090 


1.3 I .0410 


5 


7 


1 .1230 


15-9 


1-3005 


33-5 


60 


I .OIOO 


1.4 I.0420 


5 


8 


1-1255 


16.2 


1 .3030 


33-7 



444 



SOLUTIONS OF PURE ALUMINUM SULPHATE 



445 



Specific Gravity of Solutions of Pure Aluminum Sulphate at 6o° F. 

From Beveridge 





100 liters of sulphate of alumina solution contain 


Specific 






Kilos sulphate with 


gravity 


A1 2 3 kilos 


S0 3 kilos 


















14 per cent 


15 per cent 


17 per cent 








A1 2 3 


Al 2 O s 


A1 2 3 


I.005 


0.14 


0-33 


I 


0-9 


0.8 


I .016 


0.42 


0.98 


3 


2 


8 


2.5 


I .026 


0.70 


1.63 


5 


4 


7 


4-1 


I.036 


0.98 


2.28 


7 


6 


5 


5-8 


I -045 


1 .26 


2-94 


9 


8 


4 


7-4 


1 -OSS 


1-54 


3-59 


11 


10 


3 


9.1 


1 .064 


1.82 


4.24 


13 


12 


1 


10.7 


1.073 


2 .10 


4.89 


15 


14 





12.3 


1 .082 


2.38 


5-55 


17 


i5 


9 


14.0 


1 .092 


2.66 


6.20 


19 


17 


7 


15-6 


1 .101 


2-94 


6.85 


21 


19 


6 


17-3 


1 .110 


3.22 


7-5° 


23 


21 


5 


18.9 


1 .119 


3-5o 


8.16 


25 


23 


3 


20.6 


1. 128 


3-78 


8.81 


27 


25 


2 


22 .2 


I-I37 


4.06 


9.46 


29 


27 


1 


23 -9 


1 -145 


4-34 


10. 11 


31 


28 


9 


25-5 


1 -154 


4.64 


10.76 


33 


30 


8 


27-3 


1-163 


4.90 


11 .42 


35 


32 


7 


28.8 


1 .172 


5-i8 


12 .07 


37 


34 


5 


3°-4 


1. 181 


5-46 


12 .72 


39 


36 


4 


32.1 


1 .190 


5-74 


I3-38 


4i 


38 


3 


33-7 


1. 198 


6.02 


14 03 


43 


40 


1 


35-4 


1 .207 


6.30 


14.68 


45 


42 





37-o 


1. 215 


6.58 


15-33 


47 


43 


9 


38.7 


1 .224 


6.86 


15-99 


49 


45 


7 


40.3 


1.232 


7.14 


16 .64 


5i 


47 


6 


42.0 


1 .240 


7.42 


17.29 


53 


49 


5 


43-6 


1 .248 


7.70 


17-94 


55 


5i 


3 


45-3 


1.256 


7-98 


18.59 


57 


53 


2 


46.9 


1.265 


8.26 


19-25 


59 


55 


1 


48.5 


1.273 


8.54 


19.90 


61 


56 


9 


50.2 


1. 281 


8.82 


20.55 


63 


58 


8 


5i-8 


1.289 


9.10 


21 .20 


65 


60 


7 


53-5 


1.297 


9-38 


21.86 


67 


62 


5 


55-i 


i-3°5 


9-66 


22.51 


69 


64 


4 


56.8 


1.312 


9-94 


23.16 


7i 


66 


3 


58.4 


1.320 


10.22 


23-81 


73 


68 


1 


60.0 


1.328 


10.50 


24.47 


75 


70 





61.7 


1-335 


10.78 


25.12 


77 


7i-9 


63-4 



446 



APPENDIX 



Volumes SO2 Dissolved by One Volume of Water 



























so 2 


cent 


2§ 


3 


3i 


4 


4f 


5 


5i 




6| 


7 


At 
























o°C. 


1.6 


2 .O 


2.4 


2.8 


3-2 


3-6 


4.0 


4-4 


4.8 


5-2 


5-6 


10° Cr 


1 -13 


1. 41 


i-7 


2 .O 


2 .26 


2-55 


2.83 


3-ii 


3-4 


3-68 


3-96 


iS° C. 


o-9S 


1. 18 


1 .42 


1.66 


I.89 


2.13 


2-37 


2.60 


2.84 


3-07 


3 -31 


20° C. 


0.79 


O.99 


1. 18 


1.38 


1.58 


1.77 


I.97 


2.17 


2.36 


2.56 


2.76 


30° c. 


o.54 


O.68 


0.82 


o.95 


I.09 


1 .22 


I.36 


1.50 


1.63 


1.77 


1 .90 


4o°C. 


0.38 


O.47 


0.56 


0.66 


0-75 


0.85 


O.94 


1.03 


1 -13 


1 .22 


1.32 



























so 2 


7i 


8 


81 


9 


9i 


10 


io| 


12 


14 


15 


16 


At 
























o°C. 


6.0 


6.38 


6.78 


7.2 


7.6 


8.0 


8.38 


9-58 


11 .17 


11.97 


12.77 


io°C. 


4-25 


4-53 


4.81 


5-o 


5.28 


5.66 


5-94 


6.79 


7.92 


8-49 


9.06 


iS° C. 


3-55 


3-7« 


4.02 


4-36 


4-59 


4-73 


4-97 


5-67 


6.62 


7 . 10 


7-57 


20° C. 


3.00 


3-i.S 


3-35 


3-55 


3-74 


3-94 


4-i3 


4-73 


5-5b 


5-9i 


6.30 


3°°C. 


2.04 


2.18 


2.31 


2-45 


2.58 


2 .72 


2.86 


3.26 


3-7o 


4.08 


4-35 


4o°C. 


1. 41 


1.48 


1.58 


1.69 


1.79 


1.88 


1.97 


2.26 


2.63 


2.82 


3.00 



Per cent 
S0 2 


17 


18 


20 


22 


24 


26 


28 


30 


35 


40 


45 


At 
























o°C. 


13 -56 


14.36 


15.96 


17-55 


19-15 


20.74 


22 .32 


23-94 


27-93 


31-92 


35-91 


io°C. 


9.62 


10.2 


11.32 


12.45 


13-58 


14.71 


15-84 


16.98 


1981 


22 .64 


25-47 


i5° C. 


7-94 


8.57 


9 46 


10.40 


n-35 


12 .29 


13-24 


14.22 


ib. 58 


18.92 


21 .28 


20°C. 


6.69 


7.09 


7.88 


8.66 


9-45 


10.24 


11.03 


11.82 


13-79 


I5-76 


17-73 


30°C. 


4.62 


4-89 


5-44 


5-98 


6.52 


7.07 


7.61 


8.16 


9-52 


10.88 


12.24 


4o°C. 


3-i9 


3-38 


3-76 


4i3 


4-5i 


4.88 


5.26 


5-64 


6.58 


7-52 


8.46 



Per cent 
S0 2 


50 


55 


60 


65 


70 


75 


80 


85 


90 


95 


100 


At 
























o°C. 


39-9° 


43-89 


47-88 


53-67 


55-86 


59-85 


63.64 


67.63 


71.82 


75.81 


79-8 


io°C. 


28.30 


3i-i3 


33 96 


36-79 


39.62 


42-45 


45.28 


48.4 


5o.97 


53-77 


56.6 


15° C. 


23-65 


26.01 


28.38 


3°-74 


33-n 


35-47 


37-84 


40.20 


42-57 


44-99 


47-3 


2O C. 


19.70 


21 .67 


23.64 


25-6l 


27-58 


29-55 


31-53 


33-5o 


35.46 


37-43 


39-4 


30°C. 


13.60 


14.96 


16.32 


17.68 


19.04 


20.40 


21 .76 


23.12 


24.46 


25.82 


27.2 


4 o°C. 


9 -40 


10.34 


11.28 


12 .12 


13.16 


14.20 


15-04 


15.98 


16.92 


17.86 


18.8 



COMPARISON OF TEMPERATURES 



447 



CONVERSION OF CENTIGRADE TO FAHRENHEIT DEGREES 



°c. 


°P. 


+°C. 


+°F. 


+°C. 


+°F. 


+°C. 


+°F. 


+°C. 


+°F. 


-30 


— 22 .0 


17 


62.6 


64 


147.2 


in 


231-8 


158 


316.4 


29 


20.2 


18 


64.4 


65 


149.0 


112 


233-6 


159 


318.2 


28 


18.4 


19 


66.2 


66 


150.8 


113 


235-4 


160 


320.0 


27 


16.6 


20 


68.0 


67 


152.6 


114 


237.2 


161 


321.8 


26 


14.8 


21 


69.8 


68 


154-4 


115 


239.0 


162 


323-6 


25 


13.0 


22 


71 .6 


69 


156.2 


116 


240.8 


163 


325-4 


24 


11 .2 


23 


73-4 


70 


158.0 


117 


242 .6 


164 


327.2 


23 


9-4 


24 


75-2 


7i 


159.8 


118 


244.4 


165 


329.0 


22 


7.6 


25 


77.0 


72 


161. 6 


119 


246.2 


166 


33°-8 


21 


5-8 


26 


78.8 


73 


i63-4 


120 


248.0 


167 


332-6 


20 


4.0 


27 


80.6 


74 


165.2 


121 


249.8 


. 168 


334-4 


19 


2 .2 


28 


82.4 


75 


167.0 


122 


251.6 


169 


336.2 


l8 


0.4 


29 


84.2 


76 


168.8 


123 


253-4 


170 


338.o 


17 


+ 1-4 


3° 


86.0 


77 


170.6 


124 


255-2 


171 


339-8 


l6 


3-2 


3i 


87.8 


78 


172.4 


125 


257.0 


172 


341.6 


15 


5-o 


32 


89.6 


79 


174.2 


126 


258.8 


173 


343-4 


14 


6.8 


33 


91.4 


80 


176.0 


127 


260.6 


174 


345-2 


13 


8.6 


34 


93-2 


81 


177-8 


"128 


262 .4 


175 


347 -o 


12 


10.4 


35 


95-0 


82 


179.6 


129 


264.2 


176 


348.8 


II 


12 .2 


36 


96.8 


83 


181. 4 


130 


266.0 


177 


35°-6 


IO 


14.0 


37 


98.6 


84 


183.2 


131 


267.8 


178 


352-4 


9 


15. 8 


38 


100.4 


85 


185.0 


132 


269.6 


179 


354-2 


8 


17.6 


39 


102 .2 


86 


186.8 


*33 


271.4 


180 


356.o 


7 


19.4 


40 


104.0 


87 


188.6 


134 


273.2 


181 


357-8 


6 


21 .2 


4i 


105.8 


88 


190.4 


135 


275.0 


182 


359-6 


5 


23.0 


42 


107 .6 


89 


192 .2 


136 


276.8 


183 


361.4 


4 


24.8 


43 


109.4 


90 


194.0 


137 


278.6 


184 


363-2 


3 


26.6 


44 


in .2 


91 


195.8 


138 


280.4 


185 


365 


2 


28.4 


45 


113.0 


92 


197.6 


139 


282 .2 


186 


366.8 


1 


30.2 


46 


114. 8 


93 


199.4 


140 


284.0 


187 


368.6 





32.0 


47 


116. 6 


94 


201 .2 


141 


285.8 


188 


37o.4 


+ 1 


33-8 


48 


118. 4 


95 


203 .0 


142 


287.6 


189 


372.2 


2 


35-6 


49 


120.2 


96 


204.8 


143 


289.4 


190 


374-o 


3 


37-4 


5° 


122 .0 


97 


206.6 


144 


291 .2 


191 


375-8 


4 


39-2 


5i 


123.8 


98 


208.4 


145 


293.0 


192 


377-6 


S 


41 .0 


52 


125.6 


99 


210.2 


146 


294.8 


193 


379-4 


6 


42.8 


53 


127.4 


100 


212 .0 


147 


296.6 


194 


381.2 


7 


44.6 


54 


129.2 


IOI 


213.8 


148 


298.4 


195 


383 


8 


46.4 


55 


131. 


102 


215.6 


149 


300.2 


196 


384.8 


9 


48.2 


56 


132.8 


103 


217.4 


150 


302 .0 


197 


386.6 


10 


50.0 


57 


134.6 


104 


219.2 


151 


303-8 


198 


388.4 


11 


5i-8 


58 


136-4 


105 


221 .0 


152 


305-6 


199 


390.2 


12 


53-6 


59 


138.2 


106 


222.8 


153 


307-4 


200 


392.o 


13 


55-4 


60 


140.0 


107 


224.6 


154 


309.2 






14 


57-2 


61 


141. 8 


108 


226.4 


155 


311 .0 






15 


59-° 


62 


143.6 


109 


228.2 


156 


312.8 






16 


60.8 


63 


145-4 


no 


230.0 


157 ' 


314-6 







_ Reprinted from D. Van Nostrand's Chemical Annual, Fourth Issue, 191S, with the permis- 
sion of the editor and publishers. 



44 8 



APPENDIX 



(Reprinted from D. Van Nostrand's Chemical Annual, Fourth Issue, 1918, with the permis- 
sion of the editor and publishers.) 

PHYSICAL CONSTANTS 



Name 



Aluminium 

Antimony 

Argon, gas 

liquid 

Arsenic, amorph... 

cryst 

Barium 

Bismuth 

Boron, amorph. . . . 

cryst 

Bromine, gas 

liquid 

Cadmium 

Caesium 

Calcium 

Carbon, amorph... 

graphite 

diamond 

Cerium 

Chlorine, gas 

liquid 

Chromium 

Cobalt [bium) 

Columbium (Nio- 

Copper 

Erbium 

Fluorine, gas 

liquid 

Gadolinium. ....... 

Gallium 

Germanium 

Glucinum (Beryl- 
Gold [Hum) 

Helium, gas 



Sym- 
.bol 



Al 
Sb 



A 

As 

As 

Ba 

Bi 

B 

B 

Br 2 

Br 2 

Cd 

Cs 

Ca 

C 

C 

C 

Ce 

CI 

CI 

Cr 

Co 

Cb 

Cu 

Er 

F 

F 

Gd 

Ga 

Ge 

Gl 

Au 

He 



Atomic 
weight. 
= i6 



27.I 

I20.2 

39-88 

39-88 
74.96 
74.96 

137-37 
208 

11 .0 

11 .0 
.79-92 

79.92 
112.40 
132.81 

40.07 
1 2 . 005 
1 2 . 005 
1 2 . 005 
140.25 



35 
35 
52 
58 
93 

63 
167 

!9 

19 

i57 
69 
72 

9 
197 



4.00 



Molec- 
ular 
weight 



39-i 



299.84 
299 . 84 



159.84 

I59-84 
112 .40 



70.92 



38. 
38. 



4.00 



Specific Gravity. 

Water = 1. 

Air=i (A). 

Hydrogen =1 (D.) 



/ 2 . 708 

12.72V- 
6.6 9 oo¥° 
/ 1-379 A. 1 
I19.96 D.J 
t 4046- 1860 

716 140 

727 140 

75 

7474 

45 

53-2-68 

8691 600 A. 



6 4 2 17C 

87 200 



75-2.10 
10-2.585 

47-3-5585 
92 250 
491 00 A. 

44°5°° 
92 20 
7i8¥° 
o6is° 

91-8.96 

77 
31 150 A. 

I4 -187° 
31 

95 24 2 ° o 
46928 
85 200 
19.32 

/ 0.1368 A. 
11.98 D. 



Atomic 

vol. 
At.wt 



Sp.Gr. 



IO.oi 
9.96 



0.2220 
0.0495 
O.1233 



28.4 

i5-9 
13- 1 
36.6 
21.3 

4-5 
4.2 



O.O758/ 2I° — 

0.0830 1 65 ° 



24.9 
13.0 

71 .0 

25-9 
6.2 

5-i 

3-4 

20.3 



24.6 
7.6 
6.8 

13.2 

7-i 
35-i 



16.7 
120. 1 
11. 8 
13-3 
4-9 
10.2 

29.21 
20.2 / 



Specific 

heat 
at 0° C. 



03013 
O.3066 
0.l65( 210 ) 

0-0555(83°) 
0.1071 
O.0548 
0.0522 

O.I453 

O.241 

O.202 

1469 
O.05112 

1 241 
O.2262 
O.10394 
O.IO30 



0.0936 



O.079 
O.0737 



0.0316 



I.2482 1 



PHYSICAL CONSTANTS OF THE ELEMENTS 



449 



OF THE ELEMENTS 



u 

B 


•2,3 ■ 


Electrical 
conduc- 
tivity! 
at o c C. 


Thermal 

conductivity 

K* at o° C. 

Ag=i.oo 


Linear coefficient of 
expansion 


Melting 
point, 
°C. 


Boiling 

point, 

°C. 


I 

2 

3 

4 
5 
6 


6.02 

5-95 
4.92 


324000 
27100 


■3435 
.0442 

•043894 


.O4245 
.O4II52 


At °C. 

40-° 

40° 


657° 
630 ° 
-187. 9° 


>2200° 
1440° 
-l86. 1° 










5-69 

6.23 


28600 




.O4O559 


40° 




< 3 6o° 

554° 

vol. 950 
1420° 
sublimes at 






sublimes at 
850 
268 ° 
2200 in 
vacuo 


7 

8 

9 










6.27 

3-37 
1.82 

4-44 
8-57 
6.16 

6-93 

5-83 
2.89 
2 .22 
1 .76 
6.28 
4.40 
8.02 
5-42 
6.08 


9260 


.0177 


.04 1 346 


40° 
f 








{ 


3500° 






















-7-3° 
321 

28.45° 
805 ° 

sublimes at 
sublimes at 
sublimes at 

635° 
— 102 ° 


58.7 

765-9 

670 


13 
15 


146000 

25400 
95000 


.2213 


.O43069 
.O339482 


40° 
27-100 








.O4O54 


40° 
40 ° 
40 ° 


35oo ° 
35oo° 
35oo ° 


i7 
t8 






.O4O786 






.O4OI18 


19 


13950 












"33-6° 








.O21978 


0-10 










1520 

1478° 
1950 
fio8 3 ° 
1 1065 ° (in air) 


2200 


23 

24 

25 

"6 


83200 




.O4I236 


40 ° 










5-95 


640600 


.7198 


.O41678 


40 ° 


2310°, 2000 
in vacuo 


27 
*8 


























-223 


-187 


29 

3° 
3 T 












5-53 
5-34 

6.23 










30.15° 
916 
1280 
1062 ° 

< — 269° 












vol. 1350 
>i9oo 
2530 , 2000 
in vacuo 

-268. 75 




54100 200 
468000 








33 


.7003 
.033386 


.O4I470 


o-ioo 













* K = the number of grams of water which can be raised from o° to 1° C. by the heat which 
passes through a cubic centimeter of the substance in one second when the temperature of the 
opposite sides of the cube are maintained at a difference of l° C. 

t Reciprocal of the resistance in ohms of a centimeter cube of the substance. 



45° 



APPENDIX 



PHYSICAL CONSTANTS 



Name 



Sym- 
bol 



Atomic 
weight. 
= i6 



Molec- 
ular 
weight 



Specific Gravity. 

Water = I. 

Air=i (A). 

Hydrogen = i (D.) 



Atomic 

vol. 
At.wt. 



Sp.Gr. 



Specific 

heat 
at o° C. 



Hydrogen, gas. 
liquid 



3 
4 
5 
6 

7 
8 

9 

io 
ii 

12 

13 

14 
IS 
16 

17 
18 

19 

20 
21 
22 

23 

24 

25 
26 

27 
28 
29 
3° 
31 
32 

33 
34 
35 
36 
37 
38 

39 
40 



Indium 

Iodine, gas 

solid 

Iridium, spongy. 

crystalline .... 
Iron, pure 

wrought 

steel 

gray pig 

white pig. 

Krypton, gas. . . 

liquid 

Lanthanum 

Lead 

Lithium 

Magnesium 

Manganese 

Mercury 

Molybdenum. . . 
Neodymium. . . . 

Neon 



Nickel 

Nitrogen, gas. . . 

liquid 

Osmium 

Oxygen, gas. . . . 

liquid 

Ozone 

Palladium 

Phosphorus, yel. 

red 

liquid 

Platinum 

Potassium 

Praseodymium. . 

Radium 

Rhodium 

Rubidium 



Fe 
Fe 
Fe 
Fe 
Fe 

Kr 

Kr 

La 

Pb 

Li 

Mg 

Mn 

Hg 

Mo 

Nd 

Ne 

Ni 

N 

N 

Os 

O 

O 

3 

Pd 

P 

P 

P 

Pt 

K 

Pr 

Ra 

Rh 

Rb 



1 .008 

1 .008 

114. 8 
126.92 
126.92 
193- 1 
193- 1 

55-84 

55-84 

55- 

55- 

55-84 

82.92 

82 .92 
139.0 
207 .20 
6.94 

24.32 

54-93 
200.6 

96.0 
144-3 



14.01 
14.01 
190.9 
16.00 
16.00 



2 .016 
2 .016 



253-84 



82 .92 



200.6 



28.02 



32 .00 
32 .00 

48.00 



106.7 
31-04 
3*-°4 
3!-°4 
195 
39.10 
140.9 
226.0 
102 .9 
85-45 



124.16 
124.16 



0.06949 A. 

—252.83° 

O.O7IO5 
745.52 mi „ 

mm. 
7.12¥ 

8.72 A. 

4.948 170 
15-86 
22 .42 

7-85-7-88 

7.86 

7 . 60-7 . 80 

7.03-7.13 

7-58-7-73 
/2.818 A.\ 
l 40. 78 D. J 

2.155- 1520 

6-1545 
"■337i£H 

o.534 200 

i-69-i-75 

7.42 

13 -5953 s 
10 . 281^ 

6.9563 

r 0.695 A. 1 

I9.96 D.J 

8.6-8.93 

0.96737 A. 

o.8o42- 195 - 5 ° 
22 .48 

1. 10535 A. 

i.ii8i- 182 - 5 ° 

1.658 A. 
1 1 . 4-1 1 . 9 

1.831 180 

2.296 160 

i.764 44 - 3 ° 
2i.i6¥° 

0.8621 200 

6-4754 



1.4 
16. 1 



25-7 
12 .2 
8.6 
7-i 
7-i 
7-3 
7-9 
7-3 



3 -4io 



0.05695 

0.0336 2060 

0.04852 



0.0323 
1162 
1130 

0.1066 



0.1050 



38.5 
22.6 

18.3 
13.00 
14. 1 

7-4 
14.8 

9-3 



04485 
0310 
8366 
0.2456 
0.1217 
0.03346 
0.0659 



i-53 2 







6.7 


0.1084 




0.2438 


17-4 

8-5 




0.031 13 




0.2175 


14-3 






9.2 


0.0592 


17 .0 


0.202 


13-5 


0.1829 


17.6 
9.2 




0.0323 


44-7 


0.1729 


21.8 





8.5 
55-78 



0.05803 

0.0802 



PHYSICAL CONSTANTS OF THE ELEMENTS 



451 



OF THE ELEMENTS 



u 

6 




Electrical 
conduc- 
tivityf 
at o° C. 


Thermal 

conductivity 

K* at o° C. 

Ag=i.oo 


Linear coefficient of 
expansion 


Melting 
point, 

°c, 


Boiling 
point, 
°C. 


T 


3-44 
6.05 

6.56 
4.27 
6.16 




.O33270 




At°C. 


-259° 


-252. 5° 


?. 








3 


II9SOO 




. O441 7 


40° 


155° 


700 ° 






S 
6 






.O4837 


— 190-17 


II4. 2° 

2250° 

I9SO° 

IS30 

l600° 

1375° 
1275° 

1075° 

-169 


184.3S 








7 


6.23 
6.50 
6.32 
5-96 

5-87 






.O4O700 


40 ° 

o°-ioo° 
o°-ioo° 
o°-ioo° 

40 ° 




8 



13 IOOO 


.1665 
.2070 
.1300 


.O4I182 
.O4II 
.O4II 
.O4I061 


2450 ° 


10 


63000 
1 I0200- 
\ I 1300 




TT 




T2 


.1490 






13 






-iSi-7° 












TS 


6.23 

352 
5.86 
5 -98 
6.70 
6.69 
6-33 










8io° 

327°' 

186 

650 

1260 

-38. 85 . 

2500° 

840 ° 

-253° 

145 2 ° 

-210. 5 




16 

17 
18 

19 
20 
2T 


50400 
I I 9000 
230000 


.0836 


.O42924 


40 

o°-i8o° 
40 ° 


1525° 

>i400° 

1120 

1900 

357-33° 


.3760 


.O42694 


10630 


.0148 


.O3182 


o°-ioo° 


?.?. 












23 

24 












-243° 


6.36 

3-42 


144200 


.1420 
•O4524 


.O4I279 


40 


?5 


-195-5° 


afi 








21 


5-95 
3-48 


105300 




.O40657 


40 


2700 

-227 




^ 


•O4563 




-182. 7 


20 








^0 












decomp. 270 
i5So° 
44. i° 
725° 


-119 


Si 


6.32 
6.26 
5-67 


97900 


.1683 


.O4II76 


40° 

o°-44° 


32 


290 
350° (yel.) 


^!S 








S4 










ss 


6.29 
6.51 


91200 
150500 


.1664 


. O40899 


40° 
o°-50° 


1753° 
63-S 
940 ° 
700 ° 
1970° 
39° 




^6 


757-5° 


S7 






S8 














^o 


5-97 






. O40850 


40° 




40 








696 ° 















45 2 



APPENDIX 



PHYSICAL CONSTANTS 



Name 



Sym- 
bol 



Atomic 
weight 
0=i6 



Molec- 
ular 
weight 



Specific Gravity. 

Water = i. 

Air=i (A). 

Hydrogen=i (D). 



Atomic 

vol. 
At. wt 



Sp. Gr. 



Specific 

heat 
at o° C. 



Ruthenium, spon. . 

melted 

cryst 

Samarium 

Scandium 

Selenium, amorph. 

monoclinic 

hexagonal 

Silicon, amorph. . . 

cryst 

Silver 

Sodium 

Strontium 

Sulphur, 

amorphous soft, 
yellow 

rhombic 

monoclinic 

plastic 

Tantalum 

Tellurium, amorph 

cryst 

Terbium 

Thallium 

Thorium, amorph. 

cryst 

Thulium 

Tin, gray 

rhombic 

tetragonal 

Titanium 

Tungsten 

Uranium 

Vanadium 

Xenon, gas 

liquid 

Ytterbium 

Yttrium 

Zinc 

Zirconium , amorph 

cryst 



Ru 

Ru 

Ru 

Sm 

Sc 

Se 

Se 

Se 

Si 

Si 

Ag 

Na 

Sr 

S 

S 

Sa 

S/3 

St 

Ta 

Te 

Te 

Tb 

Tl 

Th 

Th 

Tm 

Sn 

Sn 

Sn 

Ti 

W 

U 

V 

Xe 

Xe 
Yb 
Yt 
Zn 
Zr 
Zr 



101 .7 
101 .7 
101 .7 

150.4 
44.1 
79.2 
79.2 
79.2 
28.3 
28.3 

107.8, 

23 .00 

87.63 

32 .06 
32 .06 
32 .06 
32 .06 
32 .06 
181. 5 
127-5 
127.5 
159.2 
204.0 
232.40 
232.40 
168. s 
118. 7 
118. 7 
118. 7 
48.1 
184.0 
238.2 
5i-o 

130.2 

130.2 

173-5 
88.7 

65-37 

90.6 

90.6 



8.6 
11. 4 
12.268° 

7-7-7,* 



II. 8 
8.9 

8-3 
19.4 



O.061 I 



633-6 
633.6 
633.6 



256.48 
256.48 
256.48 
256.48 
256.48 



255 -o 

255-0 



4.26-4.28 250 

4.47 250 
4.8 250 

2.00 

2.49!°° 

10.53 

0.97I2 200 

2-54 

i-9556°° 
2 .046 

2.05-2.07°° 
1.958 
1 .92 
i 4 . 49 if° 
6.oi5 2 °° 
6.27 



18.5 
17.7 
16.5 
14.2 
11. 4 
10.2 
23.6 
34-5 

16.4 
15-6 
15.6 



0-09533 
o . 08401 



o.24 21 ° 

O.I697 220 
0-0559 

0.2813 



11.85 

n.ool? 

11.23 



5-! 
6.53-6.56 
7 . 2984 150 
4-5o 17 - 5 ° 

18.77 

18.685V 
6.025IS 

J4.22 A. 1 

1 63. 5 D.J 
3 . S2 -i».io 



65-37 



3 .8o 15 ° 
7.142 160 

4-15 
6 . 40 180 



20.4 



0.1728 
0.1809 
0.1902 
o . 0301 7 

0525 
0-0475 



17.2 
21. 1 
20.7 



0.0326 



20.3 
18.2 
16.3 
10.7 

9.8 
12.8 

8-5 



0545 
0-0559 

0559 
0.1125 
0.0336 

0280 
o . 1 240 



37-o 



23-4 

9.2 

21.8 

14.2 



0.09356 



o . 0660 



PHYSICAL CONSTANTS OF THE ELEMENTS 



453 



OF THE ELEMENTS 



u 

CD 
X> 

s 


S S & 
3&x 


Electrical 
conduc- 
tivity^ 
at 0° C. 


Thermal 

conductivity 

K* at o° C. 

Ag=i.oo 


Linear coefficient of 
expansion 


Melting 
point, 
C. 


Boiling 
point, 
°C. 












At°C. 


>i 9 5o° 

2000 ° 

2000 ° 

I350 

1200° 

50° (softens) 

i7o°-i8o° 

217 




• ? 














3 
4 
5 
6 


6.21 






.O4O963 


40° 






















7-55 
6.65 










690° 

690° 

690° 

35°°° 

35°°° 

1955° 

877-5° 


7 
8 






O43680 


40° 






9 

TO 


6.06 
4.82 
6.04 
6.47 










200-15600 

681200 

21 IOOO 

40300 




.O4O763 

.O4I921 

.O472 


40° 
40° 
o°-50° 


1420 
961.5° 
97-6° 
900 ° 

>I20° 

ignition pt. 255 

114. 5° 
119.25° 


II 

12 

13 

14 

t6 


I .OOO 
•365 








444.6 
444-6° 
444.6° 
444.6° 
444.6° 












5-54 
5.80 
6.10 
5-46 
6.69 
6.07 






•047433 
• O46413 


i3°-5o° 
40° 


17 

t8 










19 


60600 




O408 
■O41675 
. O43440 


40° 

0°-20° 


2900° 

44 6° 

452° 




1 390° 
1390° 


?T 


46600 




32 






23 

24 

25 

06 


6.65 


56800 




.O43021 


40 ° 


302° 
>i7oo° 


1280° 


































?7 


6.49 
6.65 
6.65 

5-4i 
6.18 
6.68 
5 90 










stable <2o° 
stable >i7o° 
232° 
1795° 
3267° 
800 ° 
1720° 

— 140° 




?8 










>22 7 5° 

1450-1600 


29 


76600 


.1528 


■O42234 


40° 


^T 












32 












3^ 












34 










— 109. 1 ° 


^5 












?fi 












1800° 
1250° 
419° 
1 500° 
2350° 




37 














38 
^0 


6.12 


186000 


•2653 


.O42918 


40 ° 


918° 


/|0 


5-98 

























454 



APPENDIX 



VAPOR PRESSURE OF WATER 
According to Regnault 



°c. 


p_ 


Inches of 
mercury 


Pounds 

per square 

inch 


°c. 


°F. 


Inches of 
mercury 


Pounds 

per square 

inch 


o 


32.0 


0.181 


0.0890 


42 


107 .6 


2 .404 


1 .216 


i 


33-8 


0.194 


0.0955 


43 


109.4 


2-533 


1.244 


2 


356 


0.209 


0.1025 


44 


in .2 


2.669 


1. 312 


3 


37-4 


0.224 


O.I IOO 


45 


113. 


2. 811 


1. 381 


4 


39-2 


0.240 


0.1 180 


46 


114. 8 


2-959 


1-454 


5 


41 .0 


0.257 


0.1263 


47 


116. 6 


3-H4 


1-530 


6 


42.8 


0.276 


O.I354 


48 


118. 4 


3.276 


1 .609 


7 


44.6 


0.295 


0.1452 


49 


120.2 


3-444 


1 .692 


8 


46.4 


0.316 


O.I55I 


50 


122 .0 


3.62 


1.78 


9 


48.2 


0-338 


0.1657 


5i 


123.8 


3-8i 


1.87 


IO 


50.0 


0.361 


0.1773 


52 


125.6 


4.00 


1 .96 


ii 


51.8 


0.386 


0.1893 


53 


127.4 


4.20 


2 .06 


12 


53-6 


0.412 


0.2023 


54 


129.2 


4.41 


2.17 


13 


55-4 


0-439 


0.2158 


55 


131-0 


463 


2 .27 


14 


57-2 


0.469 


0.2303 


56 


132.8 


4-85 


2-39 


15 


59-0 


O.500 


0.2456 


57 


134-6 


5-09 


2.50 


16 


60.8 


0-533 


0.2618 


58 


136.4 


5-33 


2 .62 


17 


62.6 


0.568 


0.2789 


59 


138.2 


5-59 


2-75 


18 


64.4 


0.605 


0.2970 


60 


140.0 


5-86 


2.88 


19 


66.2 


0.644 


0.3162 


61 


141. 8 


6.14 


3.01 


20 


68.0 


0.685 


0.3363 


. 62 


143.6 


6.42 


3.16 


21 


69.8 


0.728 


0.3577 


63 


145-4 


6.72 


3 30 


22 


71 .6 


0-774 


0.3802 


64 


147.2 


7.04 


3-46 


23 


73-4 


0.822 


. 4040 


65 


149.0 


7 36 


3-62 


24 


75-2 


O.873 


0.4289 


66 


150.8 


7.70 


3-78 


25 


77.0 


0.927 


0.4554 


67 


152.6 


8.05 


3-95 


26 


78.8 


0.984 


0.4833 


68 


154-4 


8.41 


4-13 


27 


80.6 


I.944 


0.5126 


69 


156.2 


8-79 


4-32 


28 


82.4 


1 .106 


0.5434 


70 


158.0 


9.18 


4-51 


29 


84.2 


1 .172 


0.5759 


7i 


159.8 


9-58 


4-7i " 


3° 


86.0 


1 .242 


0.6101 


72 


161. 6 


10.00 


4.91 


31 


87.8 


I.3I5 


0.6461 


73 


163.4 


10.44 


512 


32 


8 9 .6 


1.392 


0.6838 


74 


165.2 


10.89 


5-35 


33 


91.4 


1-473 


0.7234 


75 


167.0 


11.36 


5-58 


34 


93-2 


1-558 


0.7655 


76 


168.8 


11.84 


5.82 


35 


95 


1.647 


0.810 


77 


170.6 


12-35 


6.06 


36 


96.8 


1.740 


0.855 


78 


172.4 


12.87 


6.32 


37 


98.6 


1.838 


0.903 


79 


174.2 


13-40 


6.58 


38 


100.4 


1. 941 


0.954 


80 


176.0 


13.96 


6.85 


39 


102 .2 


2.049 


1 .007 


81 


177-8 


14 -54 


7.14 


40 


104.0 


2.162 


1 .061 


82 


179.6 


15-14 


7-44 


4i 


105.8 


2.280 


I .121 


83 


181. 4 


15-75 


7-74 



Reprinted from D. Van Nostrand's Chemical Annual, Fourth Issue, 1918, with the permis- 
sion of the editor and publishers. 



VAPOR PRESSURE OF WATER 



455 



VAPOR PRESSURE OF WATER {Continued) 



°c. 


°F. 


Inches of 
mercury 


Pounds 

per square 

inch 


C. 


°F. 


Atmos- 
pheres 


Pounds 

per square 

inch 


84 


183.2 


16.39 


8.05 


129 


264.2 


2.592 


38.II 


8S 


185.O 


I7-05 


8-37 


130 


266.0 


2 . 


671 


39.26 


86 


186.8 


17-73 


8.71 


131 


267.8 


2 . 


753 


40.47 


87 


188.6 


18.43 


9 05 


132 


269.6 


2 . 


836 


41.68 


88 


190.4 


19.16 


941 


133 


271.4 


2 . 


921 


42.93 


89 


192.2 


19.91 


9.78 


134 


273.2 


3 


008 


44.21 


90 


194.O 


20.69 


10.16 


135 


275.0 


3 


097 


45-52 


9 1 


195.8 


21.49 


10.56 


136 


276.8 


3 


188 


46.87 


92 


197.6 


22.31 


io.95 


137 


278.6 


3 


282 • 


48.24 


93 


199.4 


23.17 


n.38 


138 


280.4 


3 


378 


49 65 


94 


20I .2 


24.04 


n. 81 


139 


282 .2 


3 


476 


51.06 


95 


203 .O 


24-95 


12 .26 


140 


284.0 


3 


576 


52.55 


96 


204.8 


25.89 


12 .71 


141 


285.8 


3 


678 


54-07 


97 


206.6 


26.85 


13-19 


142 


287.6 


3 


783 


55-6o 


98 


208.4 


27.85 


13.68 


143 


289.4 


3 


890 


57i6 


99 


2I0.2 


28.87 


14.18 


144 


291 .2 


4 


000 


58.79 






J 29-92 
l 1. 000* 




145 


293.0 


4 


113 


60.44 


100 


2I2.0 


14.70 


146 


294.8 


4 


227 


62.13 


101 


213.8 


1 .036* 


15-23 


147' 


296.6 


, 4 


344 


63.86 


102 


215.6 


1.074* 


15-79 


148 


298.4 


4 


464 


65.62 


103 


217.4 


1 .112* 


i6.35 


149 


300.2 


4 


587 


67.41 


104 


219.2 


1. 152* 


16.94 


150 


302 .0 


4 


712 


69.26 


1 OS 


221 .O 


1. 193* 


17-53 


iSi 


303-8 


4 


840 


71.14 


106 


222 .8 


1-235* 


18.15 


152 


305-6 


4 


971 


73.06 


107 


224.6 


1.278* 


18.78 


153 


307.4 


5 


104 


75.02 


108 


226.4 


1 .322* 


19.44 


154 


309.2 


5 


240 


77-03 


109 


228.2 


1.368* 


20.11 


155 


311-0 


5 


380 


79.07 


no 


23O.O 


i-4i5* 


20.80 


156 


312.8 


5 


522 


81 .22 


III 


23I.8 


1.463* 


21.51 


157 


314.6 


5 


667 


83.29 


112 


233-6 


i-5i3* 


22 .24 


158 


316.4 


• 5 


815 


85-47 


n.3 


235-4 


1.564* 


22 .99 


159 


318.2 


5 


966 


87.69 


114 


237.2 


1. 616* 


23.76 


160 


320.0 


6 


.120 


89.96 


us 


239.0 


1 .670* 


24-55 


161 


321.8 


6 


.278 


92.27 


116 


240.8 


1 .726* 


25-73 


162 


323-6 


6 


•439 


94-63 


117 


242 .6 


1.782* 


26 .20 


163 


325.4 


6 


• 603 


97.04 


118 


244.4 


1. 841* 


27 .06 


164 


327.2 


6 


•770 


99-50 


119 


246.2 


1 .901* 


27.94 


.165 


329.0 


6 


•940 


102 .01 


120 


248.0 


1 .962* 


28.85 


166 


330.8 


7 


•114 


104.56 


121 


249.8 


2 .025* 


29.78 


167 


332-6 


7 


.291 


107.18 


122 


251.6 


2 .091* 


3° -73 


168 


334-4 


7 


•472 


109.84 


123 


253-4 


2.157* 


31.70 


169 


336.2 


7 


.656 


112-53 


124 


255-2 


2 .225* 


32.70 


170 


338.o 


7 


.844 


115.29 


125 


257.0 


2.295* 


33-72 


171 


339-8 


8 


.036 


118. n 


126 


258.8 


2 .366* 


34.78 


172 


341.6 


8 


• 231 


120.98 


127 


260.6 


2.430* 


35-86 


173 


343-4 


8 


•430 


123.90 


128 


262 .4 


2.515* 


36.97 


174 


345-2 


8.632 


126.87 








♦Atrnc 


spheres. 











456 



APPENDIX 



VAPOR PRESSURE OF WATER {Continued) 



°c. 


°F. 


Atmos- 
pheres 


Pounds 

per square 

inch 


°C. 


°F. 


Atmos- 
pheres 


Pounds 

per square 

inch 


175 


347 -o 


8.839 


129.91 


203 


397-4 


16.364 


240.54 


176 


348 


8 


9.049 


133.OO 


204 


399-2 


16.703 


245-49 


177 


35° 


6 


9.263 


136.15 


205 


401 .0 


17.047 


250.53 


178 


352 


4 


9.481 


139-35 


206 


402 .8 


17.396 


255.67 


179 


354 


2 


9-703 


142.62 


207 


404.6 


17-751 


260.88 


180 


356 





9.929 


145-93 


208 


406.4 


18. Ill 


266.18 


181 


357 


8 


10.150 


I49-32 


209 


408.2 


18.477 


271-55 


182 


359 


6 


10.394 


152.77 


210 


410.0 


18.848 


277.01 


183 


361 


4 


10.633 


156.32 


211 


411. 8 


19 .226 


282.58 


184 


363 


2 


10.876 


I59-84 


212 


4136 


19.608 


288.21 


185 


365 





11. 123 


163.47 


213 


415-4 


19.997 


293.92 


186 


366 


8 


H-374 


167.17 


214 


417.2 


20.391 


299 . 72 


187 


368 


6 


11 .630 


170.94 


215 


419.0 


20.791 


305.57 


188 


37° 


4 


11.885 


174.76 


216 


420.8 


21 .197 


3«-57 


189 


372 


2 


12.155 


178.65 


217 


422 .6 


21 .69O 


317.62 


190 


374 





12.425 


182.61 


218 


424.4 


22 .027 


323-78 


191 


375 


8 


12 .699 


186.63 


219 


426.2 


22.452 


330.0I 


192 


377 


6 


12.977 


190.72 


220 


428.0 


22.882 


336-30 


193 


379 


4 


13 .261 


194.88 


221 


429.8 


23-3I9 


342.70 


194 


381 


2 


13 • 549 


199-13 


222 


431-6 


23.761 


349.21 


195 


383 





13.842 


203.43 


223 


433-4 


24.2IO 


355-81 


196 


384 


8 


14-139 


207.81 


224 


435-2 


24.666 


362.50 


197 


386 


6 


14.441 


212 .25 


225 


437 -o 


25 .128 


369 • 29 


198 


388 


4 


14-749 


216.77 


226 


438.8 


25-596 


376.17 


199 


39° 


2 


15 .062 


221.37 


227 


440.6 


26.071 


383-15 


200 


392 





15-380 


226.04 


228 


442.4 


26.552 


390.22 


201 


393 


8 


15-703 


230.79 


229 


444.2 


27.O4O 


397-40 


202 


395-6 


16.031 


235-6i 











SODIUM CHLORIDE SOLUTION AT 15 ° 
Gerlach 



Specific 
Gravity 


Per 
cent 
NaCl 


Specific 
Gravity 


Per 
cent 
NaCl 


Specific 
Gravity 


Per 

cent 
NaCl 


Specific 
Gravity 


Per 
cent 
NaCl 


1 .00725 
1. 01450 
1 .02174 
1 .02899 
1 .03624 
I .04366 
I .05108 


I 
2 

3 
4 
5 
6 

7 


I. 05851 
I.06593 

1-07335 
I .08097 
I.08859 
I .09622 
1-10384 


8 

9 
10 
11 
12 
13 
14 


1 .11146 
1 .11938 
1 .12730 
1 13523 
I-I43I5 
1-15107 

I-I593I 


15 
16 

17 
18 

19 
20 
21 


1 16755 
i-i758o 
1 .18404 
1 .19228 
1 . 20098 
1 . 20433 


22 

23 

24 

25 
26 

26.395 



Reprinted from D. Van Nostrand's Chemical Annual, Fourth Issue, 1918, with the permis- 
son of the editor and publisher. 



SODIUM CARBONATE SOLUTION AT 15' 



457 



SODIUM CARBONATE SOLUTION AT 15° 

Lunge 











1 liter contains grams 


Specific 


Degrees 
Baume 


Per cent 
Na 2 C0 3 


Per cent 
Na 2 C0 3 .io H 2 






Gravity 














Na 2 C0 3 . 


Na 2 C0 3 .io H 2 


1 .007 


1 .0 


0.67 


I.807 


6.8 


18.2 


1 .014 


2.0 


i-33 


3.S87 


13-5 


36.4 


1 .022 


3-1 


2.09 


5-637 


21 .4 


57-6 


1 .029 


4.1 


2.76 


7-444 


28.4 


76.6 


1.036 


5-1 


3-43 


9.251 


35-5 


95-8 


I 045 


6.2 


4.29 


11.570 


44.8 


120.9 


1.052 


7.2 


4-94 


I3-323 


52.0 


140.2 


1 .060 


8.2 


5-7i 


15 .400 


60.5 


163.2 


1 .067 


9.1 


6-37 


17.180 


68.0 


183.3 


1 075 


10. 1 


7 .12 


19.203 


76.5 


206.4 


I.083 


11 .1 


7.88 


21 .252 


85.3 


230.2 


1 .091 


12 .1 


8.62 


23.248 


94 


253-6 


1 .100 


13.2 


9-43 


25-432 


103.7 


279.8 


1. 108 


14. 1 


10.19 


27.482 


112 .9 


304'5 


1 .116 


151 


10.95 


29-53 2 


122.2 


329.6 


1. 125 


16. 1 


11. 81 


3I-85I 


132.9 


358.3 


I 134 


17. 1 


12 .61 


34.009 


143 


385.7 


1 .142 


18.0 


13.16 


35-493 


150.3 


405-3 


1. 152 


19. 1 


14.24 


38.405 


164. 1 


442.4 



Reprinted from D. Van Nostrand's Chemical Annual, Fourth Issue, 1918, with the permis 
sion of the editor and publishers. 



458 



APPENDIX 



CONCENTRATED SODIUM CARBONATE SOLUTION AT 30° 

Lunge 











1 liter contains grams 


Specific 


Degrees 


Per cent 


Per cent 






Gravity 


Baume 


Na 2 C0 3 


Na 2 C0 3 .io H 2 


Na 2 C0 3 


Na 2 C0 3 .io H 2 


1 .142 


18.O 


13-79 


37.21 


157-5 


425.0 


1.152 


19. 1 


14.64 


39-51 


168.7 


455-2 


1 .162 


20.2 


15-49 


41-79 


180.0 


485.7 


1 .171 


21 .2 


16.27 


43-89 


i9°-5 


514.0 


1. 180 


22.1 


17.04 


45-97 


201 .1 


542.6 


1 .190 


23.I 


17.90 


48.31 


214.0 


577-5 


1 .200 


24.2 


18.76 


50.62 


225.1 


607.4 


1 .2IO 


25.2 


19.61 


52.91 


237-3 


640.3 


T.220 


26.1 


20.47 


■ 55-29 


249.7 


673.8 


I-23I 


27.2 


21 .42 


57.8o 


263.7 


7II-5 


I .241 


28.2 


22.29 


60.15 


276.6 


746.3 


1.252 


29.2 


23-25 


62.73 


291 .1 


785.4 


I.263 


30.2 


24.18 


65.24 


305-4 


824.1 


I.274 


31.2 


25.11 


67.76 


3I9-9 


863.2 


I.285 


32.2 


26.04 


70.28 


334-6 


902.8 


1.297 


33-2 


27.06 


73.02 


35i-o 


947.1 


I.308 


34-i 


27.97 


75-48 


365-9 


987.4 



Reprinted from D. Van Nostrand's Chemical Annual, Fourth Issue, 1918, with the permis- 
sion of the editor and publishers. 



BAUME AND SPECIFIC GRAVITY 



459 



EQUIVALENT OF DEGREES BAUME (AMERICAN STANDARD) 
AND SPECIFIC GRAVITY AT 60 ° F. 

Degrees Baume = 145 — ~ — p — f° r Liquids Heavier than Water 



Degrees 


Specific Deg 


rees 


Specific Degi 


■ees 


Specific Deg 


■ees 


Specific 


Baume 


Gravity Bau 


me 


Gravity Bau 


me 


Gravity Bau 


me 


Gravity 


O.O 


I .0000 


7 


I .0262 


4 


1-0538 


I 


I.0829 




1 


I .0007 


8 


I .0269 


5 


I -054S 


2 


I.0837 




2 


1 .0014 


9 


I .0276 


6 


I-0553 


3 


I.0845 




3 


I. 0021 4 





I .0284 


7 


1-0561 


4 


1-0853 




4 


1 .0028 


1 


I .0291 


8 


I.0569 


5 


I. 0861 




5 


1-0035 


2 


I .0298 


9 


I.0576 


6 


I .0870 




6 


I .0042 


3 


I . 0306 8 





I.0584 


7 


I.0878 




7 


1 . 0049 


4 


I -0313 


1 


1.0592 


8 


I.0886 




8 


1 OOS5 


5 


I .0320 


2 


I 0599 


9 


1 . 0894 




9 


1 .0062 


6 


I .0328 


3 . 


I.0607 I2 





1 . 0902 


I 





1 .0069 


7 


1-0335 


4 


1. 0615 


1 


1 .0910 




1 


1 .0076 


8 


I.0342 


5 


I .0623 


2 


1 .0919 




2 


1 . 0083 


9 


1 0350 


6 


I . 0630 


3 


1 .0927 




3 


1 . 0090 5 





I-0357 


7 


I.0638 


4 


I-0935 




4 


1 .0097 


1 


LO365 


8 


I . 0646 


5 


I.0943 




5 


1-0105 


2 


I.0372 


9 


I.0654 


6 


I.0952 




6 


I .0112 


3 


I.0379 9 





I .0662 


7 


1 .0960 




7 


I .0119 


4 


I.0387 


1 


I.0670 


8 


I .0968 




8 


1 .0126 


S 


I -0394 


2 


I .0677 


9 


I.0977 




9 


1-0133 


6 


I . 0402 


3 


I.0685 13 





I.0985 


2 





1 .0140 


7 


I . 0409 


4 


1.0693 


1 


1.0993 




1 


I. 0147 


8 


I. 0417 


5 


I .0701 


2 


I .1002 




2 


1. 0154 


9 


I .0424 


6 


1 . 0709 


3 


I .IOIO 




3 


1.0161 6 





I.0432 


7 


I .0717 


4 


1 .1018 




4 


1. 0168 


1 


I -0439 


8 


1.0725 


5 


I .1027 




S 


1. 0175 


2 


I.0447 


9 


I-0733 


6 


I • 1035 




6 


1-0183 


3 


I.0454 IO 





1. 0741 


7 


1. 1043 




7 


1 .0190 


4 


I .0462 


1 


I.0749 


8 


1-1052 




8 


1. 0197 


5 


I .0469 


2 


I-0757 


9 


1 . 1060 




9 


1 .0204 


6 


I .0477 


3 


I .0765 14 





1 . 1069 


3 





1 .0211 


7 


I . 0484 


4 


I.0773 


1 


1 .1077 




1 


1. 0218 


8 


I .0492 


5 


I .0781 


2 


I. 1086 




2 


1 .0226 


9 


I .0500 


6 


1 .0789 


3 


I . 1094 




3 


1 -°?33 7 





I .0507 


7 


1.0797 


4 


1.1103 




4 


1 . 0240 


1 


1-0515 


8 


1 . 0805 


5 


I .nil 




5 


1 .0247 


2 


I .0522 


9 


1. 0813 


6 


1 .1120 


.6 


1-0255 


3 


I.0530 II 





1 .0821 


7 


1 .1128 



Reprinted from D. Van Nostrand's Chemical Annual, Fourth Issue. 1918. with the permis- 
sion of the editor and publishers. 



460 



APPENDIX 



EQUIVALENT OF DEGREES BAUME (AMERICAN STANDARD) 
AND SPECIFIC GRAVITY AT 6o° F. {Continued) 



Degrees 


Specific Degi 


•ees 


Specific Degi 


■ees 


Specific Deg- 


rees 


Specific 


Baume 


Gravity . Bau 


me 


Gravity Bau 


me 


Gravity Bau 


me 


Gravity 


.8 


1.1137 


2 


1. 1526 


6 


1. 1944 28 


.0 


1-2393 




9 


1. 1145 


3 


1 -1535 


7 


I-I954 


.1 


1 . 2404 


15 





1. "54 


4 


1 -1545 


8 


1 .1964 


.2 


1 .2414 




1 


1 .1162 


5 


1 -1554 


9 


I-I974 


•3 


1.2425 




2 


1 .1171 


6 


1-1563 24 





1 . 1983 


•4 


1 . 2436 




3 


1.1180 


7 


I-I572 


1 


I 1993 


•5 


1 . 2446 




4 


1.1188 


8 


1.1581 


2 


1 .2003 


.6 


1-2457 




5 


1.1197 


9 


1.1591 


3 


1 .2013 


• 7 


1 . 2468 




6 


1. 1 206 20 





1 .1600 


4 


I .2023 


8 


1.2478 




7 


1 .1214 


1 


. 1 .1609 


5 


1 . 2033 


9 


1 . 2489 




8 


1 .1223 


2 


1 .1619 


.6 


1 . 2043 29 





1 . 2500 




9 


1 .1232 


3 


1. 1628 


7 


1-2053 


1 


1-2511 


16 





1 . 1 240 


4 


1-1637 


8 


I . 2063 


2 


1.2522 




1 


1 . 1 249 


5 


1-1647 


9 


1 . 2073 


3 


1.2532 




2 


1-1258 


6 


1-1656 25 





1 . 2083 


4 


1-2543 




3 


1 .1267 


7 


1. 1665 


1 


1 . 2093 


5 


1-2554 




4 


1. 1275 


8 


1-1675 


2 


1 .2104 


6 


1.2565 




5 


1 .1284 


9 


1. 1684 


3 


I .2114 


7 


1.2576 




6 


1. 1293 21 





1 .1694 


4 


1 .2124 


8 


1.2587 




7 


1 .1302 


1 


1-1703 


5 


1. 2134 


9 


1.2598 




8 


1.1310 


2 


1 .1712' 


6 


1. 2144 30 





1 . 2609 




9 


1.1319 


3 


1 .1722 


7 


1. 2154 


1 


1 .2620 


17 





1. 1328 


4 


1.1731 


8 


1 .2164 


2 


1 .2631 




1 


1 -1337 


5 


i-i74i 


9 


1. 2175 


3 


1 . 2642 




2 


1-1346 


6 


1. 1750 26 





I. 2185 


4 


1.2653 




3 


1 -1355 


7 


1 .1760 


1 


1. 2195 


5 


1 . 2664 




4 


1-1364 


8 


1 .1769 


2 


1 .2205 


6 


1.2675 




S 


1 -1373 


9 


I.I779 


3 


1 .2216 


7 


1 . 2686 




6 


1.1381 22 





1. 1789 


4 


1 .2226 


8 


1.2697 




7 


i-i39° 


1 


1. 1798 


5 


I .2236 


9 


1.2708 




8 


1 1399 


2 


1. 1808 


6 


I.2247 31 





1. 2719 




9 


1 .1408 


3 


1.1817 


7 


1.2257 


1 


1.2730 


18 





1.1417 


4 


1. 1827 


8 


1 .2267 


2 


1.2742 




1 


1 .1426 


5 


1-1837 


9 


1 .2278 


3 


1-2753 




2 


1 -1435 


6 


1. 1846 27 





1.2288 


4 


1.2764 




3 


1 . 1444 


7 


1. 1856 


1 


1 .2299 


5 


1-2775 




4 


i-*453 


8 


1. 1866 


2 


1 . 2309 


6 


1.2787 




S 


1 .1462 


9 


1. 1876 


3 


1-2319 


7 


1 .2798 




6 


1-1472 23 





1. 1885 


4 


1.2330 


8 


1 . 2809 




7 


1 .1481 


1 


1-1895 


5 


1 . 2340 


9 


1 .2821 




8 


1 . 1490 


2 


1 . 1905 


6 


1-2351 32 





1.2832 




9 


1. 1499 


3 


1.1915 


7 


1 .2361 


1 


1 . 2843 


19 





1.1508 


4 


1. 1924 


8 


1.2372 


2 


1.2855 




1 


1-1517 


5 


1 1934 


9 


1 • 2383 


3 


1.2866 



BAUME AND SPECIFIC GRAVITY 



461 



EQUIVALENT OF DEGREES BAUME (AMERICAN STANDARD) 
AND SPECIFIC GRAVITY AT 6o° F. (Continued) 



Degrees 


Specific Degi 


•ees 


Specific Degi 


ees 


Specific Degi 


•ees 


Specific 


Baume 


Gravity Bau 


me 


Gravity Bau 


me 


Gravity Bau 


me 


Gravity 


•4 


I .2877 


8 


1. 3401 


2 


I.3969 


6 


1-4588 




5 


I . 2889 


9 


I-34I4 


3 


I-3983 


7 


1 .4602 




6 


I.2900 37 





1.3426 


4 


I.3996 


8 


1. 4617 




7 


I .2912 


1 


I-3438 


5 


I .4010 


9 


I.4632 




8 


I.2923 


2 


1 -345i 


6 


I .4023 46 





I .4646 




9 


1-2935 


3 


I-3463 


7 


I 4037 


1 


1 .4661 


33 





I . 2946 


4 


1-3476 


8 


I .4050 


2 


1 .4676 




1 


I.2958 


5 


1.3488 


9 


I .4064 


3 


1 .4691 




2 


I .2970 


6 


1. 3501 42 





I .4078 


4 


1 .4706 




3 


I .2981 


7 


I-35I4 


1 


I .4091 


5 


1. 4721 




4 


I . 2993 


8 


I-3526 


2 


I .4105 


6 


I-4736 




5 


I.3004 


9 


1-3539 


3 


I .4119 


7 


1 -4751 




6 


I. 3016 38 





1 -3551 


4 


I-4I33 


8 


1 .4766 




7 


I .3028 


1 


1-3564 


5 


I .4146 


9 


1. 4781 




8 


I.3040 


2 


1-3577 


6 


I .4160 47 





1.4796 




9 


I-305r 


3 


1-3590 


7 


I-4I74 


1 


1 .4811 


34 





I.3063 


4 


1 .3602 


8 


I. 4188 


2 


1 .4826 




1 


I-3°75 


5 


1-3615 


9 


I .4202 


3 


1 .4841 




2 


I.3087 


6 


1.3628 43 





I .4216 


4 


I-48S7 




3 


1.3098 


7 


1-3641 


1 


I.4230 


5 


1.4872 




4 


I.3110 


8 


I-3653 


2 


I.4244 


6 


1.4887 




S 


I .3122 


9 


1.3666 


3 


I.4258 


7 


1 .4902 




6 


i-3i34 39 





1.3679 


4 


I .4272 


8 


1 .4918 




7 


1-3146 


1 


1.3692 


5 


I .4286 


9 


1 -4933 




8 


1-3158 


2 


I-3705 


6 


I.4300 48 





1.4948 




9 


1-3170 


3 


i-37i8 


7 


I-43I4 


1 


1.4964 


35 





1. 3182 


4 


1 -3731 


8 


I.4328 


2 


1.4979 




1 


I-3I94 


5 


1-3744 


9 


1-4342 


3 


1-4995 




2 


1 .3206 


6 


1-3757 44 





I-4356 


4 


1. 5010 




3 


1-3218 


7 


1.3770 


1 


1 -4371 


5 


1 .5026 




4 


1.3230 


8 


I-3783 


2 


1-4385 


6 


1-5041 




S 


1.3242 


9 


1.3796 


3 


1-4399 


7 


I-5057 




6 


1.3254 40 





1-3810 


4 


I-44I4 


8 


I-5073 




7 


1 .3266 


1 


1-3823 


5 


1 .4428 


9 


1.5088 




8 


1.3278 


2 


1.3836 


6 


1 .4442 49 





1-5104 


1 


9 


1. 3291 


3 


1.3849 


7 


1-4457 


1 


1. 5120 


36 





1-3303 


4 


1.3862 


8 


I-447I 


2 


I-5I36 




1 


I-33I5 


5 


1.3876 


9 


1 . 4486 


3 


I-5I52 




2 


1-3327 


6 


1.3889 45 





1.4500 


4 


1-5167 




3 


I-3329 


7 


1.3902 


1 


I-45I5 


5 


i-5i83 




4 


1-3352 


8 


1. 3916 


2 


1.4529 


6 


I-5I99 




5 


1-3364 


9 


1.3929 


3 


1-4544 


7 


I-52I5 




6 


1-3376 41 





1-3942 


4 


I.4558 


8 


1-5231 




7 


I-3389 


1 


1-3956 


5 


1-4573 


9 


1-5247 



APPENDIX 
HYDROCHLORIC ACID 



Be. ° 


Sp. gr. 


Tw. ° 


Percent 
HC1 


Be. ° 


Sp. gr. 


Tw. c 


Percent 
HC1 


Be. ° 


Sp. gr. 


Tw. ° 


Percent 
HC1 


I.OO 


1.0069 


1.38 


1.40 


16.0 


1 . 1240 


24.80 


24-57 


20.8 


1-1675 


3350 


32.93 


2.00 


1. 0140 


2.80 


2.82 


16. 1 


1 . 1248 


24 


96 


24-73 


20.9 


1 . 1684 


33 


68 


33 


12 


3-00 


1.0211 


4.22 


425 


16.2 


1 . 1256 


25 


12 


24.90 


21.0 


1 . 1694 


33 


88 


33 


31 


4.O0 


1.0284 


5-68 


5-69 


16.3 


1 . 1265 


25 


3o 


25.06 


21. 1 


1 . 1703 


34 


06 


33 


So 


500 


10357 


7-14 


7-15 


16.4 


1 - 1274 


25 


48 


25-23 


21.2 


I-I7I3 


34 


26 


33 


69 


5-25 


1.0375 


7-5o 


7-52 


16. 5 


1 . 1283 


25 


66 


25-39 


21.3 


1 . 1722 


34 


44 


33 


88 


5.5o 


10394 


7.88 


7.89 


16.6 


1 . 1292 


25 


84 


25 .56 


21.4 


1 • 1732 


34 


64 


34 


07 


5-75 


1. 0413 


8.26 


8.26 


16.7 


1 - 1301 


26 


02 


25.72 


21.5 


1 . 1741 


34 


82 


34 


26 


6.00 


1.0432 


8.64 


8.64 


16.8 


1.1310 


26 


20 


25 89 


21.6 


1 ■ i75i 


35 


02 


34 


45 


6.25 


1.0450 


9.00 


9.02 


16.9 


1.1319 


26 


38 


26.05 


21.7 


1 . 1760 


35 


20 


34 


64 


6.50 


1.0469 


9-38 


9.40 


17.0 


1 . 1328 


26 


56 


26.22 


21.8 


1. 1770 


35 


40 


34 


83 


6.75 


1.0488 


9.76 


9-78 


17. 1 


1 • 1336 


26 


72 


26.39 


21.9 


1 1779 


35 


58 


35 


02 


7.00 


1.0507 


10.14 


10.17 


17.2 


1 - 1345 


26 


90 


26.56 


22.0 


1 ■ 1789 


35 


78 


35 


21 


725 


1.0526 


10.52 


10.55 


17-3 


1 ■ 1354 


27 


08 


26.73 


22.1 


1. 1798 


35 


96 


35 


40 


7-5o 


10545 


10.90 


10.94 


17-4 


1 - 1363 


27 


26 


26.90 


22.2 


1 . 1808 


36 


16 


35 


59 


7-75 


1.0564 


11.28 


11.32 


17-5 


1 ■ 1372 


27 


44 


27.07 


22.3 


1.1817 


36 


34 


35 


78 


8.00 


1.0584 


11.68 


11. 71 


17.6 


1 . 1381 


27 


62 


2724 


22.4 


1 . 1827 


36 


54 


35 


97 


8.25 


1.0603 


12.06 


12.09 


17-7 


1 1390 


27 


80 


27.41 


22.5 


1. 1836 


36 


72 


36 


16 


8.50 


1.0623 


12.46 


12.48 


17.8 


1 ■ 1399 


27 


98 


27-58 


22.6 


1 . 1846 


36 


92 


36 


35 


8.75 


1.0642 


12.84 


12.87 


17-9 


1 . 1408 


28 


16 


27-75 


22.7 


1 . 1856 


37 


12 


36 


54 


9.00 


1.0662 


13-24 


13 26 


18.0 


1.1417 


28 


34 


27.92 


22.8 


1 . 1866 


37 


32 


36 


73 


9-25 


1. 0681 


13-62 


13 .65 


18. 1 


1 . 1426 


28 


52 


28.09 


22.9 


1187S 


37 


5o 


36 


93 


9So 


1. 0701 


14.02 


14.04 


18.2 


1 ■ 1435 


28 


7o 


28.26 


230 


1. 1885 


37 


70 


37 


14 


9-75 


1. 0721 


14.42 


14-43 


18.3 


1 • 1444 


28 


88 


28.44 


231 


1. 1895 


37 


90 


37 


36 


10.00 


1. 0741 


14.82 


14-83 


18.4 


1 1453 


29 


06 


28.61 


232 


1 . 1904 


38 


oS 


37 


58 


10.25 


1. 0761 


15-22 


15-22 


18.5 


1 . 1462 


29 


24 


28.78 


233 


1.1914 


38 


28 


37 


80 


10.50 


1. 0781 


15- 62 


15-62 


18.6 


1.1471 


29 


42 


28.95 


23-4 


1 ■ 1924 


38 


48 


38 


03 


10.75 


1.0S01 


16.02 


I6.OI 


18.7 


1 . 1480 


29 


60 


29 13 


23-5 


1 ■ 1934 


38 


68 


38 


26 


11.00 


1. 0821 


16.42 


16.41 


18.8 


1 . 1489 


29 


78 


29.30 


236 


1 . 1944 


38 


88 


38 


49 


11.2s 


1. 0841 


16.82 


16.81 


18.9 


1 . 1498 


29 


96 


29.48 


23-7 


1 ■ 1953 


39 


06 


38 


72 


11.50 


1. 0861 


17.22 


17.21 


19.0 


1 . 1508 


30 


16 


29.65 


23.8 


1 ■ 1963 


39 


26 


38 


95 


11-75 


1. 0881 


17,62 


I7.6I 


19. 1 


1.1517 


30 


34 


29.83 


23-9 


1 • 1973 


39 


46 


39 


18 


12.00 


1.0902 


18.04 


I8.OI 


19.2 


1 . 1526 


30 


52 


30.00 


24.0 


1 • 1983 


39 


66 


39 


41 


12.25 


1.0922 


18.44 


I8.4I 


19-3 


1 1535 


30 


70 


30.18 


24.I 


1 ■ 1993 


39 


86 


39 


64 


12.50 


1 0943 


18.86 


18.82 


19.4 


1 • 1544 


30 


88 


30-3S 


24.2 


1.2003 


40 


06 


39 


86 


12.75 


1.0964 


19.28 


19.22 


19-5 


1 1554 


31 


08 


30.53 


24-3 


1 ■ 2013 


40 


26 


40 


09 


13 00 


10985 


19.70 


19.63 


19.6 


1 - 1563 


31 


26 


30.71 


24-4 


1 . 2023 


40 


46 


40 


32 


13 25 


1 . 1006 


20.12 


20.04 


19-7 


1 . 1572 


31 


44 


3090 


24-5 


1 ■ 2033 


40 


66 


40 


55 


13.50 


1 . 1027 


20.54 


20.4S 


19.8 


1 . 1581 


31 


62 


3i-o8 


24.6 


1 • 2043 


40 


86 


40 


78 


13.75 


1 . 1048 


20.96 


20.86 


19.9 


1 ■ 1590 


31 


80 


31 .27 


24-7 


1 ■ 2053 


4i 


06 


41 


OI 


14.00 


1 . 1069 


21.38 


21.27 


20.0 


1. 1600 


32 


00 


31-45 


24.8 


1 . 2063 


41 


26 


4i 


24 


14- 25 


1 . 1090 


21.80 


21.68 


20.1 


1 . 1609 


32 


18 


31.64 


24.9 


1 . 2073 


4i 


46 


4i 


48 


l4-5o 


1. mi 


22.22 


22.09 


20.2 


1.1619 


32 


38 


3182 


25.0 


1 . 2083 


4i 


66 


41 


72 


14-75 


1.1132 


22.64 


22.50 


20.3 


1 . 1628 


32 


56 


32.01 


25 1 


1 . 2093 


4i 


86 


41 


99 


15 00 


1.1154 


2308 


22.92 


20.4 


1 . 1637 


32 


74 


32.19 


25-2 


1. 2103 


42 


06 


42 


30 


1525 


1.1176 


23-52 


23 33 


20 5 


1. 1647 


32 


94 


3238 


25-3 


1.2114 


42 


28 


42 


64 


15-50 


1.1197 


23.94 


23-75 


20.6 


1 . 1656 


33 


12 


32.56 


25-4 


1. 2124 


42 


48 


43 


01 


1575 


1.1219 


24.38 


24.16 


20.7 


1. 1666 


3332 


32-75 


255 


1. 2134 


42.68 


43 -40 



Specific Gravity determinations were made at 6o° F., compared with water at 6o° F. 
From the Specific Gravities, the corresponding degrees Baume were calculated by the follow- 
ing formula: 

Baume = 145 - g^ 

Baume Hydrometers for use with this table must be graduated by the above formula which 
formula should always be printed on the scale. 

Atomic weights from F. W. Clarke's table of 1901. O = 16. 



ALLOWANCE FOR TEMPERATURE 



10-15° Be. 
15-22° Be. 
22-25° Be. 



1/40° Be. or .0002 Sp. Gr. for 1° F. 
1/30° Be. or .0003 " " " 1° F. 
1/28 Be. or .00035 i° F. 



Authority — W. C. Ferguson. 

The above table was prepared under the supervision of the Manufacturing Chemists Associa- 
tion of the United States and adopted by the Association as standard for United States 
practice. Reprints of each table may be obtained from the Secretary of the Association, 84 State 
St., Boston, 



NITRIC ACID 



463 



NITRIC ACID 



Be. ° 


Sp. Gr. 


Tw. ° 


Percent 
HN0 3 


Be. ° 


Sp. Gr. 


Tw. ° 


Percent 
HNO3 


Be. ° 


Sp. Gr. 


Tw. ° 


Percent 

HNO5 


10.00 


1. 0741 


14.82 


12.86 


23.00 


1. 1885 


3770 


30.49 


36.00 


1-3303 


66.06 


52.30 


IO. 25 


1. 0761 


15.22 


13 


18 


23 


25 


1.1910 


38.20 


30 


86 


36 


25 


1-3334 


66.68 


S2.81 


IO.SO 


1. 0781 


15.62 


13 


49 


23 


5o 


1 • 1934 


38.68 


31 


21 


36 


So 


1.3364 


67.28 


53-32 


IO-7S 


1. 0801 


16.02 


13 


81 


23 


IS 


1 ■ 1959 


39-18 


31 


58 


36 


75 


1-3395 


67.90 


53.84 


II.OO 


1. 0821 


16.42 


14 


13 


24 


00 


1 . 1983 


39-66 


3i 


94 


37 


00 


1.3426 


68.52 


54-36 


II. 2S 


1. 0841 


16.82 


14 


44 


24 


25 


1 . 2008 


40.16 


32 


3i 


37 


25 


1. 3457 


69.14 


54-89 


11. So 


1. 0861 


17.22 


14 


76" 


24 


So 


1 ■ 2033 


40.66 


32 


68 


37 


50 


1.3488 


69.76 


55-43 


11.75 


1. 0881 


17.62 


IS 


07 


24 


75 


1.2058 


41.16 


33 


05 


37 


75 


1.3520 


70.40 


55-97 


12.00 


1.0902 


18.04 


15 


41 


25 


00 


1 . 2083 


41.66 


33 


42 


38 


00 


1 -3551 


71.02 


56.52 


12.25 


1.0922 


18.44 


15 


72 


25 


25 


1 . 2109 


42.18 


33 


80 


38 


25 


I-3S83 


71.66 


5708 


I2.SO 


1.0943 


18.86 


16 


OS 


25 


50 


1 ■ 2134 


42.68 


34 


17 


38 


50 


1.3615 


7230 


57-65 


12.75 


1.0964 


19.28 


16 


39 


25 


75 


1 . 2160 


43.20 


34 


56 


38 


75 


1-3647 


72.94 


58.23 


13 OO 


1.0985 


19.70 


16 


72 


26 


00 


1 . 2185 


43-70 


34 


94 


39 


00 


13679 


73.58 


58.82 


13 25 


1. 1006 


20.12 


17 


OS 


2fi 


25 


1.2211 


44.22 


35 


33 


39 


25 


1.3712 


74.24 


59-43 


13 So 


1 . 1027 


20.54 


17 


38 


26 


50 


1 . 2236 


44.72 


35 


70 


39 


50 


1-3744 


74-88 


60.06 


13-75 


1 . 1048 


20.96 


17 


71 


26 


75 


1 . 2262 


45-24 


36 


09 


39 


75 


1.3777 


75 54 


60.71 


14.00 


1 . 1069 


21 38 


18 


04 


27 


00 


1 . 2288 


45-76 


36 


48 


40 


00 


1. 3810 


76.20 


61.38 


14-25 


1 . 1090 


21.80 


18 


37 


27 


25 


1 . 2314 


46.28 


36 


87 


40 


25 


1.3843 


76.86 


62.07 


14- So 


inn 


22.22 


18 


70 


27 


50 


1 . 2340 


46.80 


37 


26 


4o 


50 


1.3876 


77.52 


62.77 


14-75 


1.1132 


22.64 


19 


02 


27 


73 


1 . 2367 


47-34 


37 


67 


40 


75 


I-3909 


78.18 


63.48 


iS-oo 


1.1154 


23 08 


19 


36 


28 


00 


12393 


47-86 


38 


06 


41 


00 


1 ■ 3942 


78.84 


64.20 


15.25 


1.1176 


23-52 


19 


70 


28 


25 


1 . 2420 


48.40 


38 


46 


41 


25 


1-3976 


79-52 


6493 


IS So 


1.1197 


23-94 


20 


02 


28 


50 


1 . 2446 


48.92 


38 


85 


41 


50 


1 . 4010 


80.20 


6567 


15-75 


1.1219 


24.38 


20 


36 


28 


75 


1 ■ 2473 


49 -46 


39 


25 


41 


75 


1.4044 


80.88 


66.42 


16.00 


1 . 1240 


24.80 


20 


69 


29 


00 


1 . 2500 


50.00 


39 


66 


42 


00 


1 . 4078 


81.56 


67.18 


16.25 


1 . 1262 


25.24 


21 


0.5 


29 


25 


1 . 2527 


50.54 


40 


06 


42 


25 


1.4112 


82.24 


679S 


16.50 


1 . 1284 


25.68 


21 


36 


29 


So 


1 ■ 2554 


51 08 


40 


47 


42 


So 


1. 4146 


82.92 


68.73 


16.75 


1 . 1306 


26.12 


21 


70 


29 


75 


1 . 2582 


51-64 


40 


89 


42 


75 


1.4181 


83.62 


6952 


17.00 


1. 1328 


26.56 


22 


04 


30 


00 


1 . 2609 


5218 


41 


30 


43 


00 


1. 4216 


84.32 


7033 


17 -25 


1 - 1350 


27.00 


22 


38 


30 


25 


1 • 2637 


52-74 


41 


72 


43 


25 


1. 4251 


85.02 


71. IS 


17.50 


1 • 1373 


27.46 


22 


74 


30 


5o 


1 . 2664 


53-28 


42 


14 


43 


50 


1.4286 


8S.72 


71.98 


17-75 


1 • 1395 


27.90 


23 


08 


30 


75 


1 . 2692 


53-84 


42 


58 


43 


75 


1. 4321 


86.42 


72.82 


18.00 


1 . 1417 


28.34 


23 


42 


31 


00 


1. 2719 


54.38 


43 


00 


44 


00 


I.43S6 


87.12 


73 67 


18.25 


1 . 1440 


28.80 


23 


77 


31 


25 


1 . 2747 


5494 


43 


44 


44 


25 


1.4392 


87.84 


74 S3 


18.50 


1 . 1462 


2924 


24 


11 


31 


50 


1 ■ 2775 


5550 


43 


89 


44 


50 


1 . 4428 


88.56 


75-40 


18.75 


1 . 1485 


29.70 


24 


47 


31 


75 


1 . 2804 


56.08 


44 


34 


44 


75 


1.4464 


89.28 


76.28 


19.00 


1 . 1508 


30.16 


24 


82 


32 


00 


1 . 2832 


56.64 


44 


78 


45 


00 


1.4500 


90.00 


77.17 


19-25 


1 • 1531 


30.62 


25 


18 


32 


25 


1 . 2861 


57-22 


45 


24 


45 


25 


1.4536 


90.72 


78.07 


19- 5o 


1 -1554 


3108 


25 


S3 


32 


50 


1 . 2889 


.57.78 


45 


68 


4.5 


50 


1-4573 


91.46 


79 03 


19-75 


1 • 1577 


31-54 


25 


88 


32 


75 


1. 2918 


58.36 


46 


14 


45 


75 


1 . 4610 


92.20 


80.04 


20.00 


1. 1600 


3200 


26 


24 


33 


00 


1 . 2946 


S8.92 


46 


58 


46 


00 


1 . 4646 


92.92 


81.08 


20.25 


1 . 1624 


32.48 


26 


61 


33 


25 


1 ■ 2975 


59 -So 


47 


04 


46 


25 


1 . 4684 


93-68 


82.18 


20.50 


1 . 1647 


32.94 


26 


96 


33 


5o 


13004 


6a. 08 


47 


49 


46 


50 


1. 4721 


94.42 


8.3 33 


20.75 


1.1671 


33-42 


27 


33 


33 


75 


1.3034 


60.68 


47 


95 


46 


75 


1-4758 


95.16 


84.48 


21.00 


1 . 1694 


33-88 


27 


67 


34 


00 


13063 


61.26 


48 


42 


47 


00 


1.4796 


95.92 


85.70 


21.25 


1.1718 


3436 


28 


02 


34 


25 


13093 


61.86 


48 


90 


47 


25 


1.4834 


96.68 


86.98 


21.50 


1.1741 


34-82 


28 


36 


34 


50 


1. 3122 


62.44 


49 


35 


47 


50 


1 . 4872 


97-44 


88.32 


21.7S 


1.176S 


35-30 


28 


72 


34 


75 


1. 3152 


63.04 


49 


83 


47 


75 


1 . 4910 


98.20 


89.76 


22.00 


I-I789 


3578 


29 


07 


35 


00 


1. 3182 


63.64 


50 


32 


4« 


00 


1.4948 


98.96 


91 35 


22.25 


1 . 1813 


3626 


29 


43 


35 


25 


1. 3212 


64.24 


5o 


81 


48 


25 


1.4987 


99-74 


93 13 


22.50 


1 • 1837 


36.74 


29 


78 


35 


5o 


1 3242 


6484 


5i 


30 


48 


5o 


1 . 5026 


100 . 52 


95-11 


22.75 


1 . 1861 


37.22 


30 


14 


35 


75 


1-3273 


65.46 


SI 


80 











Specific Gravity determinations were made at 6o° F., compared with water at 6o° P. 
From the Specific Gravities, the corresponding degrees Baume were calculated by the follow- 
ing formula: ' 

, 145 

Baume=I45 -Sp7Gr: 

Baume Hydrometers for use with this table must be graduated by the above formula, which 
formula should always be printed on the scale. 

Atomic weights from F. W. Clarke's table of 1901. O = 16. 

ALLOWANCE FOR TEMPERATURE: 

At io°-20° Be. — 1/30 Be. or .00029 Sp. Gr. = 1° F. 

20°-30° Be. — 1/23 Be. or .00044 " " = i° F. 

3o°-40° Be. — 1/20 Be. or .00060 " " = 1° F. 

40°-48.5° Be. — 1/17° Be. or .00084 " " = i° F. 

Authority — W. C. Ferguson. 

The above table was prepared under the supervision of the Manufacturing Chemists Associa- 
tion of the United States and adopted by the Association as standard for United States practice. 
Reprints of each table may be obtained from the Secretary of the Association, 84 State St., 
Boston. 



464 



APPENDIX 



AQUA AMMONIA 



Be. ° Si 


). Gr. 


Per cent 
NH 3 


Be. ° Si 


. Gr. 


Per cent 
NH 3 


Be. ° Si 


. Gr. 


Per cent 
NH 3 


10.00 1 


0000 


.00 


16.50 


9556 


11. 18 


23.00 


9150 


23-52 . 


10.25 


9982 


• 40 


16.75 


954o 


11.64 


23-25 


9135 


24.01 


10.50 


9964 


.80 


17.00 


9524 


12.10 


2350 


9121 


24-50 


10.75 


9947 


1. 21 


17-25 


95o8 


12.56 


23.75 


9106 


2499 


11.00 


9929 


1.62 


17-So 


9492 


13-02 


24.00 


9091 


35-48 


11.25 


9912 


2.04 


I7-7S 


9475 


13-49 


24.25 


9076 


2597 


11.50 


9894 


2.46 


18.00 


9459 


13-96 


24.50 


9061 


26.46 


11.75 


9876 


2.88 


18.25 


9444 


14-43 


24-75 


9047 


26.95 


12.00 


9859 


3-30 


18.50 


9428 


14.90 


35 00 


9032 


27.44 


12.25 


9842 


3-73 


18.75 


9412 


15-37 


35-25 


9018 


27.93 


12.50 


9825 


4.16 


19.00 


9396 


15.84 


35.50 


9003 


28.42 


I27S 


9807 


4-59 


19.25 


938o 


16.32 


35-75 


8989 


28.91 


1300 


979o 


502 


i9-5o 


936S 


16.80 


36.00 


8974 


29.40 


13-25 


9773 


5-45 


19 -75 


9349 


17.28 


26.25 


8960 


29.89 


13 5o 


9756 


5-88 


20.00 


9333 


17.76 


26.50 


8946 


30.38 


13- 75 


9739 


6.31 


20.25 


93i8 


18.24 


36.75 


8931 


30.87 


14.00 


9722 


6.74 


20.50 


9302 


18.72 


37.00 


8917 


3136 


1425 


9705 


7.17 


20.75 


9287 


19.20 


37.25 


8903 


31.85 


14 So 


9689 


7.61 


21. OO 


9272 


19.68 


37.50 


8889 


32.34 


14-75 


9672 


8.05 


21.25 


9256 


20.16 


37-75 


8875 


32.83 


15.00 


9655 


8.49 


2I.50 


9241 


20.64 


38.00 


8861 


33-32 


15 -25 


9639 


8.93 


21.75 


9226 


21.12 


38.25 


8847 


33-81 


1550 


9622 


9.38 


22.00 


921 1 


21.60 


38.50 


8833 


34 -3o 


15-75 


9605 


983 


22.25 


9195 


22.08 


28-75 


8819 


34-79 


16.00 


9589 


10.28 


22.50 


9180 


22.56 


29.00 


8805 


35-28 


16.25 


9573 


10.73 


22.75 


9165 


23.04 









Specific Gravity determinations were made at 6o° F., compared with water at 6o° F. 
From the Specific Gravities, the corresponding degrees Baume were calculated by the follow- 
ing formula: 

-o ' J 40 

Baume = 5 — ■= 130. 

bp. Gr. 

Baume Hydrometers for use with this table must be graduated by the above formula, which 
formula should always be printed on the scale. 

Atomic weights from F. W. Clarke's table of 1901. O = 16. 



ALLOWANCE FOR TEMPERATURE 

The coefficient of expansion for Ammonia Solutions, varying with the temperature, correction 
must be applied according to the following table: 



Corrections to be added for each 


Corrections to be subtracted for each degree 


degree below 6o° F. 


above 6o° F. 


Degrees 
Baume 


40° F. 


50° F. 


70° F. 


8o°F. 


90° F. 


ioo° F. 


14 


.015° Be. 


.017° Be. 


.020° Be. 


.022° Be. 


.024° Be. 


.026° Be. 


16 


.021 " 


023 " 


.026 " 


.028 " 


.030 " 


.032 " 


18 


.027 ' 


.029 ' 


031 ' 


• 033 ' 


■035 ' 


037 ' 


20° 


■033 " 


.036 ' 


■ 037 " 


.038 " 


.040 ' 


.042 ' 


22° 


•039 ' 


.042 ' 


■043 " 


• 045 ' 


047 ' 




26° 


053 " 


• 057 " 


• 057 " 


• 059 " 







Authority — W. C. Ferguson. 

The above table was prepared under the supervision of the Manufacturing Chemists Asso- 
ciation of the United States and adopted by the Association as standard for United States 
practice. Reprints of each table may be obtained from the Secretary of the Association, 84 State 
St., Boston. 



SULPHURIC ACID 



en 


u 



03 




OOT 




so 

An 


> . 

•a ° 

a M 

g-s 


S'-S.S 

<L)T aj'o 






a, 


£ 






VhJ 

Ah 


> • 

■3 ° 

el " 

O-S 


















p_ 














°F. 




O I 


0000 


0.0 


O.OO 


62.37 


O.OO 


0.00 


32.0 


37 


I . 3426 


68.5 


43-99 


8374 


47.20 


39-53 


-60 




I I 


0069 


1 


4 


I.02 


62 


80 


I 


09 


0.68 


31 2 


38 


1 -3551 


71.0 


45 


35 


84.52 


48.66 


4I-I3 


-53 




2 I 


0140 


2 


8 


2.o8 


63 


24 


2 


23 


1. 41 


30.5 


39 


I.3679 


73-6 


46 


72 


85.32 


50.I3 


42.77 


-47 




3 I 


0211 


4 


2 


3.13 


63 


69 


3 


36 


2.14 


29.8 


40 


I. 3810 


76.2 


48 


10 


86.13 


5I.6I 


44-45 


-41 




4 i 


0284 


5 


7 


4.21 


64 


14 


4 


52 


2.90 


28.9 


41 


1.3942 


78. 8 


49 


47 


86.96 


53 08 


46.16 


-35 




5 i 


0357 


7 


1 


5.28 


64 


60 


5 


67 


3-66 


28.1 


42 


1 . 4078 


81.6 


50 


87 


87.80 


54-58 


47-92 


—31 




6 i 


0432 


8 


6 


6.37 


65 


06 


6 


84 


4-45 


27.2 


43 


1. 4216 


84.3 


52 


26 


88.67 


56.07 


49.72 


-27 




7 i 


0507 


10 


1 


7-45 


65 


53 


7 


99 


5.24 


26.3 


44 


1. 43S6 


87.1 


53 


66 


89.54 


57-58 


5156 


—23 




8 i 


0584 


11 


7 


8.55 


66 


01 


9 


17 


6.06 


25.1 


45 


1.4500 


90.0 


55 


07 


90.44 


59 09 


5344 


—20 




9 i 


0662 


13 


2 


9.66 


66 


5o 


10 


37 


6.89 


24.O 


46 


1 . 4646 


92.9 


56 


48 


9135 


60.60 


55.36 


-14 




IO I 


0741 


14 


8 


I0.77 


66 


99 


11 


56 


7-74 


22.8 


47 


1.4795 


95-9 


57 


90 


92.28 


62 . 13 


57-33 


— 15 




II i 


0821 


16 


4 


II.89 


67 


49 


12 


76 


8.61 


21.5 


48 


1 ■ 4948 


990 


59 


32 


9323 


63.65 


59-34 


-18 




12 I 


0902 


18 





13 OI 


68 


00 


13 


96 


9-49 


20.0 


49 


1. 5104 


102. 1 


60 


75 


94.20 


65.18 


61.40 


—22 




13 I 


0985 


19 


7 


14-13 


68 


5i 


15 


16 


io.39 


18.3 


50 


1.5263 


105.3 


62 


18 


95.20 


66.72 


63.52 


-27 




14 I 


1069 


21 


4 


15-25 


69 


04 


16 


36 


11.30 


16.6 


51 


1 ■ 5426 


10S.5 


63 


66 


96.21 


68.31 


65.72 


—33 




IS I 


1 154 


23 


I 


16.38 


69 


57 


17 


5S 


12.23 


14- 7 


52 


1. 5591 


in. 8 


65 


13 


97.24 


69.89 


67.96 


-39 




16 i 


1240 


24 


8 


17-53 


70 


10 


18 


81 


13- 19 


12.6 


S3 


l.S76i 


115- 2 


66 


63 


98.30 


7i.5o 


70.28 


-49 




17 i 


1328 


26 


6 


18.71 


70 


65 


20 


oS 


14.18 


10.2 


54 


1-5934 


118. 7 


68 


13 


99 -38 


73 11 


72.66 


-59 




18 i 


1417 


28 


3 


19.89 


71 


21 


21 


34 


1520 


7-7 


55 


1.6111 


122. 2 


69 


65 


100.48 


74-74 


75- 10 






19 i 


1508 


30 


2 


21.07 


71 


78 


22 


61 


16.23 


4.8 


56 


1 . 6292 


125.8 


71 


17 


101.61 


76.37 


77.60 




£0 


20 I 


1600 


32 





22.25 


72 


35 


23 


87 


17.27 


+ 1.6 


57 


1 . 6477 


129- 5 


72 


75 


102 . 77 


78.07 


80.23 




■* 


21 I 


1694 


33 


9 


2343 


72 


94 


25 


14 


18.34 


- 1.8 


58 


1 . 6667 


133. 3 


74 


36 


10395 


79-79 


82.95 




tu 1 
PP ' 


22 I 


1789 


35 


8 


24.61 


73 


53 


26 


41 


19.42 


- 6.0 


59 


1.6860 


137- 2 


75 


39 


105.16 


81.54 


85-75 


- 7 




23 I 


1885 


37 


7 


25.81 


74 


13 


27 


69 


20.53 


— 11 


60 


I- 7059 


141. 2 


77 


67 


106 . 40 


8335 


88.68 


+12. 


6 


24 I 


1983 


39 


7 


2703 


74 


74 


29 


OO 


21.68 


-16 


61 


1 . 7262 


145- 2 


79 


43 


107.66 


8S.23 


91.76 


27.3 


25 I 


2083 


41 


7 


28.28 


75 


36 


30 


34 


22.87 


-23 


62 


1.7470 


149. 4 


81 


3o 


108.96 


87.24 


95.06 


39- 


1 


26 I 


2185 


43 


7 


29-53 


76 


00 


3i 


69 


24.08 


—30 


63 


1.7683 


153-7 


83 


34 


110.29 


89-43 


98.63 


46. 


1 


27 I 


2288 


45 


8 


30.79 


76 


64 


33 


04 


2532 


-39 


64 


1 . 7901 


158.0 


85 


66 


111.6s 


91.92 


102 . 63 


46. 


4 


28 I 


2393 


47 


9 


3205 


77 


3° 


34 


39 


26.58 


-49 


64i 


1-7957 


159- 1 


86 


33 


112.00 


92.64 


103.75 


43- 


6 


29 I 


2500 


5o 





33 33 


77 


96 


35 


76 


27.88 


-61 


! '-i' 


1 . 8012 


160. 2 


87 


04 


112.34 


93.4o 


104.93 


41- 


1 


30 I 


2609 


52 


2 


34.63 


78 


64 


37 


16 


29.22 


-74 


64! 


1.8068 


161. 4 


87 


81 


112.69 


94.23 


106 . 19 


37-9 


31 I 


2719 


54 


4 


35-93 


79 


33 


38 


55 


30.58 


-82 


65 


I. 8125 


162.5 


88 


65 


113-05 


95- 13 


107.54 


33- 


1 


32 I 


2832 


5<"> 


6 


37.26 


80 


03 


39 


98 


32.00 


-96 


65! 


1. 8182 


163.6 


89 


55 


113.40 


96.10 


108.97 


24. 


6 


33 1 


2946 


58 


9 


38.58 


80 


74 


41 


40 


33 42 


-97 


65; 


1 ■ 8239 


164.8 


90 


60 


113.76 


97.22 


110.60 


1.3-4 


34 1 


3063 


6l 


3 


39.92 


81 


47 


42 


83 


3490 


-91 


'">5] 


1 . 8297 


165.9 


91 


80 


114. 12 


9851 


112.42 


— I 




35 1 


3182 


63 


6 


4127 


82 


22 


44 


28 


36.41 


-81 


66 


1 • 8354 


167. 1 


93 


19 


114.47 


100.00 


114.47 -29 




36 1 


3303 


66.1 


42.63 


82.97 


45-74 


3795 


-70 



















* Calculated from Pickering's results, Journal of London Chemical Society, vol. 57, p. 363. 

F. 



Approximate Boiling Points 
50 Be., 295 F. 



6o° ' 


' 386 ' 


6i° ' 


' 400 ' 


62° ' 


' 415° ' 


6.3 U ' 


' 432° ' 


6 4 u ' 


' 451° " 


65° ' 


' 485° " 


66° ' 


' 538° ' 



Allowance for Temperature 
At 10° Be., .029° Be. or .00023 Sp. Gr. = 1° 



00034 
00039 
00041 
00045 
00053 
00057 
00054 

Specific Gravity determinations were made at 6o° F., compared with water at 60° F. 
From the Specific Gravities, the corresponding degrees Baume were calculated by the fol- 
lowing formula: 



" 20° " 


• 036° 


" 30° ' 


■035 


" 4O " 


.031° 


" 50° " 


.028° 


" 6o° " 


.026° 


" 63 " 


.026° 


" 66° " 


■0235 



Baume = 145 — 



145 



Sp. Gr. 

Baume Hydrometers for use with this table must be graduated by the above formula, which 
formula should always be printed on the scale. 

66° Baume = Sp. Gr. 1.8354. 
1 cu. ft. water at 60° F. weighs 62.37 lbs. av. 
Atomic weights from F. W. Clarke's table of 1901. O = 16. 
H 2 S0 4 = 100 per cent. 
H,S0 4 O. V. 60 ° 

O. V. 93.19 100.00 119.98 

60° 77.67 83.35 100.00 

So° 62.18 66.72 80.06 

Acids stronger than 66° Be. should have their percentage compositions determined by chemi- 
cal analysis. 

Authorities. — W. C. Ferguson; H. P. Talbot. 
_ The above table was prepared under the supervision of the Manufacturing Chemists Asso- 
ciation of the United States and adopted by the Association as standard for United States 
practice. Reprints of each table may be obtained from the Secretary of the Association, 84 State 
St., Boston. 

(46S) 



466 



APPENDIX 



COMPARISON OF METRIC AND CUSTOMARY UNITS FROM i TO 9 

1. Length 



Inches Millimeters 


Feet Meters 


Yards Meters 


(in.) (mm.) 


(ft.) (m.) 


(yd.) (m.) 


0.039 37=1 


1=0.304 801 


1=0.914 402 


0.078 74=2 


2=0.609 601 


2=1.828804 


0.118 ii=3 


3=0.914 402 


3=2.743205 


o.lS7 48=4 


4 = 1.219 202 


4=3-657607 


0.19685=5 


5 = 1.524003 


5=4.572009 


0.236 22=6 


6=1.828804 


6=5.486411 


0.275 59 =1 


7=2.133604 


7=6.400 813 


0.31496=8 


8=2.438 405 


8=7.315215 


o.354 33=9 


9=2.743205 


9=8.229616 


1= 25.4001 


3.28083=1 


1.093 6n=l 


2 = 50.8001 


6.561 67=2 


2.187 222=2 


3= 76.2002 


9.84250=3 


3.280833=3 


4 = 101.6002 


13- 123 33=4 


4.374 444=4 


5 = 127.0003 


16.404 17=5 


5.468056=5 


6 = 152.4003 


19.68500=6 


6.561 667=6 


7 = 177.8004 


22.96583=7 


7.655278=7 


8=203.2004 


26.246 67=8 


8.748889=8 


9 = 228.6005 


29 527 50=9 


9.842 500=9 



Area 



Square Square 
inches centimeters 
(sq. in.) (cm. 2 ) 


Square Square 
feet meters 
(sq. ft.) (m.2) 


Square Square 
yards meters 
(sq. yd.) (m.2) 


0.15500=1 


1=0.092 90 


1=0.8361 


0.31000=2 


2=0.18581 


2=1.6723 


0.465 oo=3 


3=0.278 71 


3=2.5084 


0.62000=4 


4=0.371 61 


4 = 3-3445 


0.775 oo=5 


5=0.46452 


5=4.1807 


0.93000=6 


6=0.55742 


6 = 5.0168 


1.08500=7 


7=0.65032 


7=5.8529 


1.24000=8 


8=0.74323 


8=6.6890 


i.395oo=9 


9=0.836 13 


9 = 7.5252 


1= 6.452 


10.764=1 


1.1960=1 


2 = 12.903 


21.528=2 


2.3920=2 


3 = 19-355 


32.292=3 


3.5880=3 


4=25.807 


43.055=4 


4.7839=4 


5=32.258 


53 819=5 


5.9799=5 


6=38.710 


64.583=6 


7.1759=6 


7=45.161 


75-347=7 


8.3719=7 


8 = 51.613 


86.111=8 


9.5679=8 


9=58.065 


96.875=9 


10.7639=9 



From Circular No. 47, U. S. Bureau of Standards. 







3. VOLUME 






Cubic Cubic 


Cubic Cubic 


Cubic Cubic 


Cubic 






feet meters 


yards meters 


inches Liters 


feet Liters 


(cm. 3 ) 


(cu. ft.) (m.3) 


(cu. yd.) (m.») 


(cu. in.) (1.) 


(cu. ft.) (1.) 


0.061 02=1 


1=0.028 317 


1=0.7646 


1=0.016 386 7 


1= 28.316 


0.12205=2 


2=0.056 634 


2=1.5291 


2=0.032 773 4 


2= 56.633 


0.18307=3 


3=0.084 95i 


3=2.2937 


3=0.049 160 2 


3= 84.949 


0.24409=4 


4=0.113 268 


4 =3 0582 


4=0.065 546 9 


4=113.265 


0.305 12 = 5 


5=0.141 585 


5=3.8228 


5=o.o8i 933 6 


5 = 141.581 


0.366 14=6 


6=0.169 9°2 


6=4.5874 


6=0.098 320 3 


6 = 169.898 


0.427 i6=7 


7=0.198 219 


7=5.3519 


7=0.114 707 


7=198.214 


0.488 19=8 


8=0.226 536 


8=6.1165 


8=0.1310938 


8 = 226.530 


0.549 21=9 


9=0.254853 


9=6.88io 


9=0.147 480 5 


9=254.846 


1= 16.3872 


35 314=1 


1.3079=1 


61.025 = 1 


0.035315=1 


2= 32.7743 


70.629=2 


2.6159=2 


122.050=2 


0.070 631=2 


3= 491615 


ioS943=3 


39238=3 


183.075=3 


0.105 946=3 


4 = 65.5486 


141.258=4 


5-2318=4 


244.100=4 


0.141 262=4 


5= 81.9358 


176.572=5 


6-5397=5 


305.125=5 


0.176577=6 


6= 98-3230 


211.887 = 6 


7.8477=6 


366.150=6 


0.211 892=6 


7=114.7101 


247.201=7 


9- 1556=7 


427.175=7 


0.247 2o8=7 


8=131.0973 


282.516=8 


10.4635=8 


488.200=8 


0.282 523=8 


9 = 147.4845 


317.830 = 9 


11.7715 = 9 


549.225=9 


o.3i7 839=9 



4. Capacity 



Liquid Measure 


Dry Measure 


U. S. Milli- 


U. S. 


U. S. 




U. S. 


fluid liters 


liquid Liters 


liquid Liters 


U. S. Liters 
gallons 
(gal.) (1.) 


ounces 

(fl. oz.) (ml.) 


pints 
(pt.) (1.) 


quarts 
(qt.) (1.) 


quarts 
(qt.) (1.) 


0.033815=1 


1=0.473 17 


1=0.94633 


0.264 i8=l 


0.9081 = 1 


0.067 629=2 


2=0.94633 


2 = 1.89267 


0.52836=2 


1.8162=2 


0.101 444=3 


3 = 1.41950 


3 = 2.83900 


o.792 53=3 


2.7243=3 


o.i35 259=4 


4 = 1.892 67 


4=3-785 33 


1.05671=4 


3.6324=4 


0.169 074=5 


5=2.36583 


5=4.731 67 


1.32089=5 


4-54oS=5 


0.202888=6 


6=2.83900 


6 = 5.67800 


1-58507=6 


5.4486=6 


0.236 703=7 


7=3.312 17 


7 = 6.62433 


1.84924=7 


6.3567=7 


0.270 518=8 


8=3-785 33 


8 = 7-57o66 


2. 113 42=8 


7.2648=8 


O-304 333=9 


9 = 4-25850 


9=8.51700 


2.37760=9 


8.1729=9 


1= 29.573 


2.1134 = 1 


1.056 71 = 1 


1= 3-785 33 


1 = 1.1012 


2= 59-146 


4.2268=2 


2. 113 42=2 


2= 7.57066 


2 = 2.2024 


3= 88.719 


6.3403 = 3 


3.170 13=3 


3 = 11.35600 


3=3-3036 


4=118.292 


8-4537=4 


4.226 84=4 


4=15.141 33 


4=4.4048 


5 = 147.865 


10.5671=5 


5283 55=5 


5 = 18.92666 


6 = 5.5060 


6=177.437 


12.6805=6 


6.340 26 = 6 


6 = 22.711 99 


6=6.6072 


7 = 207.010 


14-7939=7 


7396 97=7 


7=26.49733 


7 = 7.7084 


8=236.583 


16.9074=8 


8.453 68=8 


8 = 30.282 66 


8=8.8096 


9=266.156 


19.0208=9 


95io39=9 


9=34.06799 


9=9.9108 



From Circular No. 47, U. S. Bureau of Standards. 



(467) 



468 



APPENDIX 

5. Mass 



Troy 
ounces Grams 

(oz. t.) (g.) 


Avoirdu- 
pois Grams 
ounces 
(oz. av.) (g.) 


Avoirdu- Kilo- 
pois grams 
pounds 
(lb. av.) (kg.) 


0.032 151 = 1 


0.035 274=1 


l=o.453 59 


0.064301=2 


0.070548=2 


2=0.907 18 


0.096 452=3 


0.105 822=3 


3=1.36078 


0.128 603=4 


0.141096=4 


4=1.814 37 


0.160 754=5 


0.176 370=5 


5=2.26796 


0.192 904=6 


0.211 644=6 


6=2.721 55 


0.225055=7 


0.246 918=7 


7=3.175 15 


0.257 206=8 


0.282 192=8 


8=3.628 74 


0.289 357=9 


0.317 466=9 


, 9=4.08233 


1= 31-103 


1= 28.350 


2.204 62 =1 


2= 62.207 


2= 56.699 


4.409 24 =2 


3= 93 -3io 


3= 85.049 


6.61387 =3 


4=124.414 


4=113.398 


8.81849 =4 


5 = 155-517 


5=141.748 


11.023 ii=5 


6 = 186.621 


6=170.097 


13227 73=6 


7 = 217.724 


7=198.447 


15432 36=7 


8=248.828 


8=226.796 


17.63698=8 


9=279-931 


9=255.146 


19.841 6o=9 



From Circular No. 47, U. S. Bureau of Standards. 



INDEX 



Abietic acid, 265 
Absorbency of papers, 410 
Acid colors, 320 

in paper, determination of, 422 
sulphite cooking liquor, 160 

effect on metals, 178 

strength of, 176, 184, 190 

systems of making, 169 

testing, 209 

thiosulphuric acid in, 166 
Acids, action on cellulose, 8 
Adansonia, 40 
Adhesives for coating, 328, 331, 333, 

343; 345 
Albumen, 343 

Alcohol from soda cooks, 117 
sulphate process, 147 
sulphite process, 198, 205 
Alder, 62 

Alkali cellulose, 20 
Alum, 269, 277 

amount necessary in sizing 270, 280 

cake, composition, 278 

composition, 279 

decomposition by celluk>se, 7 

effect on glue, 259 

free acid in, 280 

iron in, 279 

manufacture, 278 

method of adding to beaters, 281 

substitutes, 269 

testing, 282, 286 

use in clarifying water, 359 
Aluminum resinate, 269 

sulphate (table), 444, 445 
Ammonia (table), 464 
Analyses, see Testing 



AniHne dyes, 313 

absorption by fillers, 314 

adding to beaters, 317 

classification of, 317 

dissolving, 317 

mordants for, 316 
Annatto, 313 
Antichlors, 244 
Antifroth oils, 329, 349 
Appendix, 444 
Asbestine, 301 

Ash, determination in papers, 414 
in fibrous materials, 415 
qualitative analysis of, 416 
Ashcroft tester, 406 
Asparagus for pulp, 44 
Aspen, 61 

B 

Bache-Wiig process for ground wood, 

222 
Backwater, use in bleaching, 239 
Bagasse, 43 
Balm of Gilead, 61 
Bamboo, 43, 86 

compositon of, 87 

pectose in, 93 

treatment recommended, 87 

yield of stems per acre, 86 
fibre, 87 
Bark, 55 

in soda process, 95 
sulphite process, 158 
Barker acid system, 173 
Barkers, 158 
Barytes, 346 
Basic colors, 318 
Basswood, 65 



469 



47° 



INDEX 



Bast fibres, 37 

Baume and specific gravity (table), 459- 

461 
Beating test for wood pulps, 372 
Beech, 62 

Binder from sulphite waste liquor, 201 
Birches, 61 
Bisulphites (see also acid), 160 

losses in preparing, 176 
Black ash, 133 

furnaces, 132, 149 
leaching tanks, 133 
waste, 135 
testing, 140 
Black gum, 65 
Black liquor, 123 

composition of. 123, 127, 147 
evaporation of, 127 
table, 444 
testing, 139 

use in sulphate process, 142 
utilization of, 125 
Blanc fixe, 346 
Bleach required by fibres, 123, 380, 381 

water, 354 
Bleached pulp, blueing of, 253 
color change on storing, 254 
oxycellulose in, 252 
washing, 246 
Bleaching, 225 
apparatus, 240 

determination of degree ot, 11 
Dobson process, 242 
effect of acid, 240, 242 
temperature, 234 
on chemical properties, 251 
strength of fibres, 249, 250 
ground wood, 244 
Hermite process, 233 
jute, 243 

principles of, 234 
rate of color change, 239 
systems, 241 
use of antichlors, 244 

backwater, 239 
weight lost on bleaching, 236 



Bleaching with chlorine gas, 226 

permanganates, 247 

peroxides, perborates, etc., 249 
Bleaching powder, 228 

action on metals, 231 

deterioration, 229, 231 

dissolving, 230 

sludge from, 230 

testing, 254 
Blow pits, 194 

tanks, 118 
Blowing down pressure, 193 
Boiler compounds, 356 

scale, 3S5 . 
Boiling wood for grinding, 219 
Bricks for digester finings, 181 
Bright's method for unbleached sul- 
phite, 393 
Bulk of fibrous materials, 65 

paper, determining, 400 
Bulker, pressure, 401 
Burgess acid system, 173 
Bursting strength of paper, 404 



Calcium hypochlorite, color of solu- 
tions, 232 
solid, 232 
Calender staining, 321 
Casein, composition, 334 

detection in paper, 418 

deterioration of, 339 

determination in paper, 425 

influence on penetration of oil, 328 

insoluble matter in, 337 

molding of, 337 

preservation of solutions, 338 

properties and preparation, 333 

sizing, 286 

soluble, 33s 

solvents, 336 

testing, 339 

waterproofing, 338, 339 
Cattle feed from waste sulphite liquor. 
• 203 



INDEX 



471 



Causticity of soda cooking liquor, 109 
Causticizing methods, 98 
Cell, structural unit of plant, 34 
Cellulose, 1 

acetates, 17 

action of salts on, 7 

and acids, 8 
alkalis, 9, 20 
ferments, 12 
water, 3 

benzoates r 19 

chlorinated, 251 

commercial meaning, 2 

composition and constitution, 2 

compound, 23 

compounds of, 13 

copper number of, n, 252 

cuto-, 23 

decomposition of, 8, 12 

destructive distillation of, 13 

determination of, 27 

esters, 18, 19 

formates, 19 

groups of, 22 

hydrates, 4 

ligno-, 24, 156 

nitrates, 13 

nitrites, 17 

normal moisture, 4 

oxidation of, 10 

pecto-, 23 

peroxide, n 

physical properties, 1 

solvents for, 5 

sulpho-carbonate, 20 

xanthate, 20 
Cement for digester linings, 180 
Chardonnet silk, 15 
Chestnut, 62 
Chips, length of, 159 
Chlorinated cellulose, 251 
Chlorine gas, 225 

in bleached fibre, 252 

in paper, 421 

preparation by electrolysis, 232 
Chrome yellow, 310 



Clark process for water softening, 357 
Clay, 294 

composition of, 295 
fineness of particles, 296 
for coating, 345 
specific gravity, 297 
testing, 297, 302 
Coated paper, 325 

body stock for, 326 
brittleness of, 440 
finish on, 329 
picking of, 328 
printing qualities, 330, 344 
waterproof, 338 
Coating, coloring of, 321 
determining amount on paper, 424 
glycerine in, 329, 349 
method of applying, 326 
minerals used, 328 
oils, soaps and waxes, 329 
Cochineal, 313 

Color standards for bleached pulp, 379, 
381 
water, 362 
Coloring, 306 

comparing colors, 307 
matching shades, 306 
mineral colors, 308, 310 
mordants, 316 
organic colors, 313 
pigments, 308 
vulcanized fibre, 323 
Colors, acid, 320 
basic, 318 
direct cotton, 317 
eosines and rhodamines, 319 
pigments, 308 
testing, 322 
Combustion chamber, 166 
Cooking liquor, testing, 137, 152, 209 
Cooking sulphite, following progress in, 
191 
irregularities in, 191 
Mitscherlich process, 183 
precautions, 186 
recording conditions, 187 



472 



INDEX 



Cooking sulphite, Ritter-Kellner pro- 
cess, 184 
schedules for, 186 
superheated steam for, 185 

Coolers for sulphur dioxide, 168 

Copper number of cellulose, n, 252 

Corn stalks, 43 

Cotton, 36 

Cotton stalks, 44 

Cottonwood, 61 

Cucumber tree, 63 

Cuprammonium hydrate cellulose, 5 

Cutch, 313 

Cuto-cellulose, 23 

Cutter for sampling wood pulps, 

. 369 
Cutting press for color disks, 376 
Cymene, 198 

D 

Daylight lamps, 307, 375, 379 
Decay of wood, 56 

effect on soda process, 95 
Defects in printing, 435 
Densities of soda stock, 122 

stock in bleaching, 234, 241 

sulphite stock, 195 
Digesters, soda, 97, 98 
sulphate, 142 
sulphite, 178 

bronze, 179 

Mitscherlich, 183 

Salomon-Briingger, 179 

sizes of, 181 
Direct cotton colors, 317 
Dirt in pulps, 383 
Disk machine for color comparisons, 

376 
District of Columbia paper tester, 

405 
Dobson bleaching process, 242 
Dolomite for acid making, 174 
Dorr causticizing process, 100 
Douglas spruce, 60 
Drying sized papers, 273 
Ducts, proportion to fibres, 392 



E 

Eau de Javel, 227 

Electrolyzing salt, 232 

Electrolytic bleach, 233 

Electrotypes, 431 

Elements, table of physical constants, 

448-453 
Enderlein's evaporator, 128 
Enge process for ground wood, 223 
Eosines, 319 
Esparto, 42, 77 

alkali required, 78 

bleaching fibre from, 79 

boilers, 78 

bulk of, 66 

cooking conditions, 79 

dust, 77 

recovery of alkali, 79 
Evaporators, Enderlein's, 128 

Torion, 127 

Yargan, 128 

Zaremba, 131 



Ferments, action on cellulose, 12 
Fert ilizer from waste sulphite liquor, 202 
Fibre length of woods, 49 
Fibres, estimation in paper, 387 

by method of Spence and Krauss, 
392 
Fibrous materials, bulk of, 65 
Fillers, 290 

absorption of dyes by, 314 

effect on sizing, 290 

effect on strength of paper, 290 

losses in process, 293 

materials used, 291 

retention of, 292, 417 

testing, 302 
Filters, 358 
Firs, 58 

Folding endurance of paper, 406 
Formaldehyde in coatings, 338 
Freeman process for soda cooks, 115 
Fuel from waste sulphite liquor, 203 



INDEX 



473 



Furfural, n 

Furnaces, recovery, 132, 149 



Gas bleaching, 226 
pressure in sulphite cooks, 188 

relieving, 189 
recovery, 192 
Gelatine, 258 

testing, 261, 332 
Glarimeter, 402 
Gloss of paper, 402 
Glue, 258 
detection of, 419 
determination of, 425 
for coating, 331 
sizing, 287 
Glycerine in coating, 329, 349 
Grease-proof qualities of paper, 412 
Grinders for wood pulp, 212, 213 
Groundwood pulp, 212 

Bache-Wiig process, 222 
bleaching, 224 
condition of stone, 216 

wood, 218 
efficiency of grinding, 219 
estimation in paper, 427 
from boiled or steamed wood, 219 
in print papers, 89 
sand settlers, 214 
screens for, 213 
speed of stones, 217 
stones for making, 212 
temperature of grinding, 218 
testing, 223 
woods for, 221 
Gun-cotton, 15 
Gypsum, 298 

H 

Halftone plates, 430 

standard depths, 431 
screens for different papers, 433 
Hardness in water, cause, 353 
determining, 364 
effect on sizing, 353 



Heartwood, 49 

Heavy spar, 301 

Hemlock, 60 

Hemp, 38 

Hermite electrolytic bleach process, 233 

Herreshoff pyrites burner, 166 

Herzberg stain, 389 

Hydrocellulose, 4, 8 

Hydrochloric acid (table), 462 

Hypochlorites, 226, 233 

Hypochlorous acid, 227 



Incinerating furnaces, 132, 149 
Indanthrenes, 321 
Ingersoll glarimeter, 402 
Ink, choice of, 434 

double tone, 442 

drying, 438 

for sizing test, 413 

mottling of, 441 

offsetting, 437 



Jute, 39 

bleaching, 243 

K 

Knots, 56, 94, 159 
Kraft fibre, 141 



Lamp black, 312 

Larch, 60 

Leaching tanks for black ash, 133 

Lignin, 25, 35, 157 

reactions with sulphurous acid, 157 

sulphonic acid, 157 
Ligno-cellulose, 24, 156 
Lime, 175 

for causticizing, 103 
rag boiling, 72 

mud testing, 138 

recovery in soda process, 102 



474 



INDEX 



Lime, slaking, 175 

testing, 138 

waste, 102 
Limestone for acid towers, 1 70 
Linen, 37 

Linings for sulphite digesters, 178 
Lithography, 432 

smutting of ink, 440 
Loading and filling, 290 
Loft drying, 260 
Logwood, 313 

M 

Machine direction, 395 
Magazine grinder, 213 
Manila hemp, 39 

bleaching, 243 
Maples, 64 
Mechanical pulp, 212 
Melt from sulphate recovery, 150 
Mercaptans, 146 
Metric and ordinary units (table) , 466- 

468 
Microscopic examination of paper, 

386 
Milk of lime acid systems, 173 
Mineral colors, 308, 310 
Mitscherlich acid tower, 169 
cooking process, 183 
digester lining, 179 
sizing process, 288 
Moisture estimation in lap pulp, 371 
paper, 414 
wood pulps, 368 
Monosulphite of calcium, 171, 176, 177, 

192 
Mordants, 316 
Morterud digester, 97 
Mullen tester, 405 
Multiple effect evaporation, 128 

N 

Newspaper, fibre from, 90 
Nitric acid (table), 463 
Nitro-cellulose, 13 



O 

Ochres, 309 

Odors from sulphate cooks, 142, 146, 151 

Offsetting, 437 

Opacity of paper, 400 

Oxide colors, 309 

Oxycellulose, 10, 252 



Padding, 321 

Paper, recovering fiber from printed, 

Paper mulberry, 41 

scales, 397, 398 
Paper testing, 386 

absorbency, 410 

acidity, 422 

ash, 414 

bulk, 400 

bursting strength, 404 

chlorine, 421 

coating, 424 

fibre content, 387 

folding endurance, 406 

gloss, 402 

grease-proof qualities, 412 

groundwood pulp, 427 

machine direction, 395 

microscopic examination, 386 

moisture, 414 

opacity, 400 

paraffin, 421 

permeability to air, 411 

physical tests, 395 

retention of filler, 417 

rosin estimation, 420 

sizing, 412, 417 

stretch, 404 

sulphur, 422 

tearing strength, 409 

tensile strength, 403 

thickness, 399 

unbleached sulphite, 393, 426 

volumetric composition, 411 

weight per ream, 397 

wire side, 396 
Papyrus, 44 



INDEX 



475 



Paraffin, determination in paper, 421 

Parchment paper, 6 

Pea vines, 44 

Pearl hardening, 299 

Peat, 45 

Pebble mills, 373 

Pecto-cellulose, 23 

Pectose, 93 

Perborates in bleaching, 249 

Permanganate bleaching, 247, 252 

Permeability of paper, 411 

Permutite water softening process, 358 

Peroxides in bleaching, 249 

Picking of coated papers, 328, 439 

Pigments, 308 

Pimaric acid, 265 

Pines, 59 

Pitch from waste sulphite liquor, 202 

Poplar, 61 

Porion evaporator, 127 

Precipitated chalk, 300 

Preston lining, 180 

Printing, 429 

defective, 435 

inks, 434 

paper for different types of, 432 
Print-papers, 88 
Prussian blue, 310 
Pyrites, 161, 166 

burner, 166 



Quercitron, 313 



R 



Rags, alkali used in boiling, 71 
bleaching, 240 
boilers for, 73 
boiling, 70 
bulk of, 65 

dusting and sorting, 70 
grades of, 68 
lime for boiling, 72 
losses in treating, 76 
starch in, 72 
washing of boiled, 75 



Recovery of sulphur dioxide, 192 
Redwoods, 313 
Register in printing, 442 
Relieving digesters, 103, 117, 189 
Resins in plant cells, 35 
woods, 53 
rubber, 288 
Retention of fillers, 292 
Rhodamines, 319 
Rinman's black liquor process, 125, 

148 
Ritter-Kellner acid towers, 170 

cooking method, 184 
Rosin, amount used in paper, 271 
detection in paper, 419 
determination in paper, 420 
extraction from stumps, 265 
in sulphite pulps, 195 
properties of, 264 
recovery from soda cooks, 117 
size making, 265 
testing, 275 
Rosin sizing, 264 

additions to, 267 
and hard water, 272 
composition, 266 
defects, 274 
effect of sunlight, 275 
emulsifier for, 268 
precipitation of, 269 
troubles, 272 
Rotogravure process, 433 
Rubber resins for sizing, 288 
Rushes, 43 



Safflower, 313 

Salomon-Briingger digester, 179 

Sand settlers, 122 

Sapwood, 49 

Satin white, composition, 347 

preparation, 348 
Schopper folding machine, 407 

tensile machine, 404 
Sedimentation test, 383 
Seed hairs, 36 



476 



INDEX 



Sizing (see also Rosin), 257 
alum used, 277 
casein, 286 
defects of, 274 
determining degree of, 412 

kind of, 417 
effect of drying, 273 
filler, 272, 291 
hard water, 353 
sunlight on, 275 
from sulphite waste liquor, 203 
glue, 287 

ink for testing, 413 
Mitscherlich process, 288 
reactions in, 270 

requirements of different papers, 257 
rosin, 264 
rubber resins, 288 
silicate-starch, 263 
starch, 262 

surface or tub sizing, 258 
viscose, 287 
Smelting furnaces, 149 
Soap in coating, 329, 349 

tub sizing, 259 
Soda process, 93 

alkali required, 115 
black liquor, no, 123 
boiling operations, 103 
caustic soda consumed, 112 
circulation of liquor, 103 
cooking liquor preparation, 98 
digesters, 97, 98 
discharging digesters, 118 
effect of caustic added, 107 
causticity of liquor, 109 
concentration of liquor, 106 
steam pressure, 104 
time under pressure, 108 
lime recovery, 102 
liquor per cord, 103 
loss of fibre, 122 
modified forms, 115, 116 
principles of, 93 
rate of reaction, no 
relief of digesters, 103, 117 



Soda process, rosin recovery, 117 
soda losses, 135 
recovery, 126 
steam lost on blowing, 119 

required, 104 
sulphur in, 115 
wash pits, 119 
washing black stock, 120 
wood preparation, 95 
woods used, 94 

yields from various woods, 114 
Soda lost in process, 135 

recovery, 126 
Sodium carbonate (tables), 457, 458 

chloride (table), 456 
Specific gravity and Baume (table), 

459-461 
Spruces, 58 

Starch, detection in paper, 418 
for coating, 343 

sizing, 262 
modified, 344 
retention, 263 
Starch-iodide indicator, 256 
Steam lost on blowing digesters, 119 
required in soda cooks, 104 
sulphite cooks, 185 
Steaming wood, 220 
Straw, 41, 80 
alkali recovery, 85 
boards, 81 
bulk of, 66 
cellulose, 84 
chlorination of, 86 
composition of, 80 
cooking, 81, 83, 86 
packing in boilers, 82 
retting, 86 
Stretch of papers, 404 
Stuffing, 321 
Sudan III, 35 
Sulphate process, 141 
black liquor, 147 
by-products from, 148 
composition of liquor, 144 
cooking, 143 



INDEX 



477 



Sulphate process, digesters, 142 
odors from, 142, 146, 151 
recovered ash, 150 
recovery furnaces, 149 
smelting furnaces, 149 
soda recovery, 149 
value of alkalies, 143 
yields, 145 
Sulphite acid (see Acid) 
fibre, composition of, 195 
process, 156 

absorption apparatus, 168 
cooking, 183, 191 
digesters and linings, 178 
modified processes, 197 
pumping acid, 177 
reactions of liquor making, 160 
storing acid, 177 
sulphur dioxide preparation, 161 
theory of, 156 
woods for, 157, 160 
"turpentine," 198 
waste liquor, 198 

alcohol from, 205 
cattle feed from, 203 
composition of, 199 
destructive distillation, 204 
fertilizer from, 202 
fuel from, 204 
pitch from, 202 
sizing, 203 

tanning materials from, 204 
testing, 210 
use as binder, 201 
volume obtainable, 200 
Sulphur, 161 

determination in paper, 422 
in soda cooks, 115 
per ton of sulphite, 193 
sublimation, 166 
testing, 207 
use of molten, 162 
Sulphur burners, 162 
air supply, 165 
automatic feed, 162 
color of flame, 166 



Sulphur burners, flat, 162 

rotary, 162 

temperatures in, 165 * 

Vesuvius, 163 
Sulphur dioxide (table), 446 

absorption apparatus, 168 

cooling, 165, 168 

preparation, 161 

recovery, 192 

solubility in water, 168, 446 
testing, 208 
Sulphur trioxide in burner gases, 

165 
Sulphuric acid (table), 465 

and cellulose, 6 
Sunlight, effect on sizing, 275 
Superheated steam for sulphite cook- 
ing, 185 
Sweet gum, 63 
Sycamore, 64 
Sylvic acid, 265 



Tables: Aluminum sulphate, 444, 445 
Ammonia, 464 

Baume and specific gravity, 459-461 
Black liquor, 444 
Hydrochloric acid, 462 
Metric and ordinary units, 466-468 
Nitric acid, 463 
Physical constants of the elements, 

448-453 
Sodium carbonate, 457, 458 
Sodium chloride, 456 
Sulphur dioxide solubility, 446 
Sulphuric acid, 465 
Temperature conversions, 447 
Vapor pressure of water, 454 
Talc, 300 

Tank systems for acid making, 171 
Tanning material from waste sulphite 

liquor, 204 
Tearing test for paper, 409 
Temperature comparisons (table), 447 
Tensile strength of paper 4.03 



478 



INDEX 



Testing acid, 209 

alum, 282, 286 

black ash and black ash waste, 140 

black liquor, 139 

bleaching powder, 254 

burner gases, 208 

caseines, 339 

clay, 297, 302 

colors, 322 

cooking liquor, 137, 152, 209 

fillers, 302 

gelatine and glue, 261, 332 

groundwood pulp, 223 

lime, 138 

lime mud, 138 

paper, 386 

rosin and rosin size, 275 

soda ash, 137 

sulphur, 207 

waste sulphite liquor, 210 

water, 359 

wood pulp, 368 
Thickness of paper, 399 
Thiosulphuric acid in sulphite liquor, 

166 
Three color work, 431 

non-register, 442 
Thwing tearing tester, 409 
Tower systems of acid making, 169 

comparison with milk of lime sys- 
tems, 175 
difficulties in operating, 171 
Tracheids, 45 
Tub sizing with gelatine, 258 

starch, 262 
Tuliptree, 63 
Turmeric, 313 
Turpentine, sulphite, 198 



U 

Ultramarine, 311 

Umber, 309 

Unbleached sulphite estimation, 393, 

426 
Ungerer's cooking process, 143 



Vapor pressure of water (table), 454 
Venetian red, 309 
Viscose, 20, 287 

silk, 21 
Volume composition of paper, 411 
Vulcanized fibre, colors for, 323 

W 

Wash pits for soda fibre, 119 
Washing black stock, 120 

bleached pulp, 246 

rag stock, 75 

sulphite fibre, 194 
Water, 351 

alum treatment, 359 

analysis, 359 

bleach consumed by, 354 

classification of, 352 

filtration, 358 

for dyeing, 316 

iron in, 353 

requirements in paper making, 75, 
3Si, 353 

sampling, 360 

scale from, 355 

soft and hard, 352, 364 

softening, 356 

suspended matter in, 354, 363 
Waterproof coated paper, 338, 343 
Waxes in coating, 329, 349 
Weight per ream, 397 
Weld, 313 

Willesden products, 6 
Winestock process for old papers, 90 
Wire side of paper, 396 
Witherite, 301 
Wood, 45 

barking, 158 

capacities of machinery for handling, 
160 

chipping, 159 

decay of, 56 

fibre length, 49 



INDEX 



479 



fibres, 45 

for grinding, 221 

kinds used, 57 

moisture in, 51 

preparing, 94, IS7 

proximate analysis, 54 

requirements for sulphite process, 157 

resins in, 53 

weight per cord, 66, 114 
cubic foot, 52 
Wood pulp testing, 368 
beating test, 372 
bleaching qualities, 380 
borer for sampling, 369 
color comparisons, 375 



Wood pulp testing, dirt count, 383 

loss in weight on bleaching, 382 
moisture determinations, 368 
sedimentation test, 383 



Yaryan evaporators, 128 
capacities, 132 



Zacaton, 44 

Zaremba evaporator, 131 

Zinc chloride and cellulose, 5 



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